add info on custom metadata for document tasks

Author: guimachiavelli

reference/api/documents.mdx

@@ -256,6 +256,7 @@ This endpoint accepts the following content types:
 | :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
 | **`primaryKey`**   | `null`        | [Primary key](/learn/getting_started/primary_key#primary-field) of the index                                                              |
 | **`csvDelimiter`** | `","`         | Configure the character separating CSV fields. Must be a string containing [one ASCII character](https://www.rfc-editor.org/rfc/rfc20). |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
 
 <Warning>
 Configuring `csvDelimiter` and sending data with a content type other than CSV will cause Meilisearch to throw an error.
@@ -378,6 +379,7 @@ This endpoint accepts the following content types:
 | :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
 | **`primaryKey`**   | `null`        | [Primary key](/learn/getting_started/primary_key#primary-field) of the documents                                                          |
 | **`csvDelimiter`** | `","`         | Configure the character separating CSV fields. Must be a string containing [one ASCII character](https://www.rfc-editor.org/rfc/rfc20). |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
 
 <Warning>
 Configuring `csvDelimiter` and sending data with a content type other than CSV will cause Meilisearch to throw an error.
@@ -451,6 +453,7 @@ curl \
 | **`function`**     | `null`        | A string containing a RHAI function                                                         |
 | **`filter`**       | `null`        | A string containing a filter expression |
 | **`context`**      | `null`        | An object with data Meilisearch should make available for the editing function |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
 
 #### `function`
 
@@ -487,6 +490,12 @@ Delete all documents in the specified index.
 | :---------------- | :----- | :--------------------------------------------------------------------- |
 | **`index_uid`** * | String | [`uid`](/learn/getting_started/indexes#index-uid) of the requested index |
 
+### Query parameters
+
+| Query Parameter    | Default Value | Description                                                                                                                             |
+| :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
+
 ### Example
 
 <CodeSamplesDeleteAllDocuments1 />
@@ -518,6 +527,12 @@ Delete one document based on its unique id.
 | **`index_uid`** *   | String         | [`uid`](/learn/getting_started/indexes#index-uid) of the requested index                |
 | **`document_id`** * | String/Integer | [Document id](/learn/getting_started/primary_key#document-id) of the requested document |
 
+### Query parameters
+
+| Query Parameter    | Default Value | Description                                                                                                                             |
+| :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
+
 ### Example
 
 <CodeSamplesDeleteOneDocument1 />
@@ -548,6 +563,12 @@ Delete a set of documents based on a filter.
 | :---------------- | :----- | :--------------------------------------------------------------------- |
 | **`index_uid`** * | String | [`uid`](/learn/getting_started/indexes#index-uid) of the requested index |
 
+### Query parameters
+
+| Query Parameter    | Default Value | Description                                                                                                                             |
+| :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
+
 ### Body
 
 A filter expression written as a string or array of array of strings for the documents to be deleted.
@@ -594,6 +615,12 @@ Delete a set of documents based on an array of document ids.
 | :---------------- | :----- | :--------------------------------------------------------------------- |
 | **`index_uid`** * | String | [`uid`](/learn/getting_started/indexes#index-uid) of the requested index |
 
+### Query parameters
+
+| Query Parameter    | Default Value | Description                                                                                                                             |
+| :----------------- | :------------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
+| **`customMetadata`** | `null`         | An arbitrary string accessible in the [generated task object](/reference/api/tasks#custommetadata) |
+
 ### Body
 
 An array of numbers containing the unique ids of the documents to be deleted.

reference/api/tasks.mdx

@@ -35,7 +35,8 @@ The `/tasks` route gives information about the progress of [asynchronous operati
   "duration": "PT0.001192S",
   "enqueuedAt": "2022-08-04T12:28:15.159167Z",
   "startedAt": "2022-08-04T12:28:15.161996Z",
-  "finishedAt": "2022-08-04T12:28:15.163188Z"
+  "finishedAt": "2022-08-04T12:28:15.163188Z",
+  "customMetadata": null
 }
 ```
 
@@ -250,6 +251,11 @@ curl \
 **Type**: String<br />
 **Description**: The date and time when the task finished `processing`, whether `failed`, `succeeded`, or `canceled`, in [RFC 3339](https://www.ietf.org/rfc/rfc3339.txt) format
 
+### `customMetadata`
+
+**Type**: String<br />
+**Description**: An arbitrary string optionally configured for `/document`-related tasks. Commonly used to keep track of which documents were processed in a specific task. 
+
 ### Summarized task object
 
 When an API request triggers an asynchronous process, Meilisearch returns a summarized task object. This object contains the following fields: