Add ephemeralStorageSizeMB option docs (#8142)

* Add ephemeralStorageSize option docs

* fix: rename ephemeralStorageSize to ephemeralStorageSizeMB

* Update src/pages/[platform]/build-a-backend/functions/configure-functions/index.mdx

Co-authored-by: josef <[email protected]>

---------

Co-authored-by: josef <[email protected]>

Author: fossamagna

src/pages/[platform]/build-a-backend/functions/configure-functions/index.mdx

@@ -69,6 +69,17 @@ export const myDemoFunction = defineFunction({
 });
 ```
 
+## `ephemeralStorageSizeMB`
+
+By default, functions have 512MB of ephemeral storage to them. This can be configured from 512 MB upto 10240 MB. Note that this can increase the cost of function invocation. For more pricing information visit the [Lambda pricing documentation](https://aws.amazon.com/lambda/pricing/).
+
+```ts title="amplify/functions/my-demo-function/resource.ts"
+export const myDemoFunction = defineFunction({
+  // highlight-next-line
+  ephemeralStorageSizeMB: 1024 // allocate 1024 MB of ephemeral storage to the function.
+});
+```
+
 ## `runtime`
 
 Currently, only Node runtimes are supported by `defineFunction`. However, you can change the Node version that is used by the function. The default is the oldest Node LTS version that is supported by AWS Lambda (currently Node 18).