add documentation for KVStoreEntry and migration guide from v2 to v3

Author: Jake Champion

documentation/docs/fastly:kv-store/KVStoreEntry/prototype/arrayBuffer.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.arrayBuffer()
+
+The `arrayBuffer()` method of the `KVStoreEntry` interface takes a `KVStoreEntry` stream and reads it to completion. It returns a promise that resolves with an `ArrayBuffer`.
+## Syntax
+
+```js
+text()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A promise that resolves with an `ArrayBuffer`.

documentation/docs/fastly:kv-store/KVStoreEntry/prototype/body.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.body
+
+The `body` read-only property of the `KVStoreEntry` interface is a `ReadableStream` of the body contents.
+
+## Value
+
+A `ReadableStream`.

documentation/docs/fastly:kv-store/KVStoreEntry/prototype/bodyUsed.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.bodyUsed
+
+The `bodyUsed` read-only property of the `KVStoreEntry` interface is a `boolean` value that indicates whether the body has been read yet.
+
+## Value
+
+A boolean value.

documentation/docs/fastly:kv-store/KVStoreEntry/prototype/json.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.json()
+
+The `json()` method of the `KVStoreEntry` interface takes a `KVStoreEntry` stream and reads it to completion. It returns a promise which resolves with the result of parsing the body text as JSON.
+
+Note that despite the method being named `json()`, the result is not JSON but is instead the result of taking JSON as input and parsing it to produce a JavaScript object.
+
+## Syntax
+
+```js
+json()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A `Promise` that resolves to a JavaScript object. This object could be anything that can be represented by JSON — an object, an array, a string, a number…

documentation/docs/fastly:kv-store/KVStoreEntry/prototype/text.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.text()
+
+The `text()` method of the `KVStoreEntry` interface takes a `KVStoreEntry` stream and reads it to completion. It returns a promise that resolves with a `String`. The `KVStoreEntry `is always decoded using UTF-8.
+
+## Syntax
+
+```js
+text()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A `Promise` that resolves with a `String`.

documentation/docs/migration-guide/index.mdx

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 pagination_prev: null
 ---
+
+# `Migrating from v2 to v3`
+
+## SimpleCache.delete renamed to SimpleCache.purge and requires purge options to be supplied as the second parameter
+
+We are renaming because "purge" is already a well-known and documented concept for removing content from Fastly's cache.
+
+The new addition of a second argument allows the caller to decide what scope to purge the content from, currently they can choose to purge from all of Fastly ("global") or from the POP that contains the currently executing instance ("pop"). We do not provide a default option right now, in the future we may provide a default option, if we discover a common pattern is being used.
+
+Here is an example of migrating an application using `SimpleCache.delete` to `SimpleCache.purge` with the same purging behaviour:
+```diff
+/// <reference types="@fastly/js-compute" />
+
+import { SimpleCache } from 'fastly:cache';
+
+addEventListener('fetch', event => event.respondWith(app(event)));
+
+async function app(event) {
+  const url = new URL(event.request);
+  const path = url.pathname;
+  if (url.searchParams.has('delete')) {
+-    SimpleCache.delete(path);
++    SimpleCache.purge(path, { scope: "global" });
+    return new Response(page, { status: 204 });
+  }
+
+  let page = SimpleCache.getOrSet(path, async () => {
+    return {
+      value: await render(path),
+      // Store the page in the cache for 1 minute.
+      ttl: 60
+    }
+  });
+  return new Response(page, {
+    headers: {
+      'content-type': 'text/plain;charset=UTF-8'
+    }
+  });
+}
+
+async function render(path) {
+  // expensive/slow function which constructs and returns the contents for a given path
+  await new Promise(resolve => setTimeout(resolve, 10_000));
+  return path;
+}
+
+
+```
+
+
 # `Migrating from v1 to v2`
 
 ## ObjectStore renamed to KVStore

documentation/versioned_docs/version-2.0.0/fastly:kv-store/KVStoreEntry/prototype/arrayBuffer.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.arrayBuffer()
+
+The `arrayBuffer()` method of the `KVStoreEntry` interface takes a `KVStoreEntry` stream and reads it to completion. It returns a promise that resolves with an `ArrayBuffer`.
+## Syntax
+
+```js
+text()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A promise that resolves with an `ArrayBuffer`.

documentation/versioned_docs/version-2.0.0/fastly:kv-store/KVStoreEntry/prototype/body.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.body
+
+The `body` read-only property of the `KVStoreEntry` interface is a `ReadableStream` of the body contents.
+
+## Value
+
+A `ReadableStream`.

documentation/versioned_docs/version-2.0.0/fastly:kv-store/KVStoreEntry/prototype/bodyUsed.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.bodyUsed
+
+The `bodyUsed` read-only property of the `KVStoreEntry` interface is a `boolean` value that indicates whether the body has been read yet.
+
+## Value
+
+A boolean value.

documentation/versioned_docs/version-2.0.0/fastly:kv-store/KVStoreEntry/prototype/json.mdx

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+---
+hide_title: false
+hide_table_of_contents: false
+pagination_next: null
+pagination_prev: null
+---
+
+# KVStoreEntry.json()
+
+The `json()` method of the `KVStoreEntry` interface takes a `KVStoreEntry` stream and reads it to completion. It returns a promise which resolves with the result of parsing the body text as JSON.
+
+Note that despite the method being named `json()`, the result is not JSON but is instead the result of taking JSON as input and parsing it to produce a JavaScript object.
+
+## Syntax
+
+```js
+json()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A `Promise` that resolves to a JavaScript object. This object could be anything that can be represented by JSON — an object, an array, a string, a number…