feat(batches): docs for auto-merge (#1170)

Documentation for
https://linear.app/sourcegraph/issue/PROD-587/enablement-experimental-auto-merge-for-github

I also removed the experimental label from "Merge" since we don't
display it as experimental in the UI anymore.

Author: bahrmichael

docs/batch-changes/bulk-operations-on-changesets.mdx

@@ -33,11 +33,12 @@ Below is a list of supported bulk operations for changesets and the conditions w
 | **Commenting**           | Post a comment on all selected changesets. Useful for pinging people, reminding them to take a look at the changeset, or posting your favorite emoji                                                                                                                                                                                                                                                     |
 | **Detach**               | Detach a selection of changesets from the batch change to remove them from the archived tab                                                                                                                                                                                                                                                                                                              |
 | **Re-enqueue**           | Re-enqueues the pending changes for all selected changesets that failed                                                                                                                                                                                                                                                                                                                                  |
-| **Merge (experimental)** | Merge the selected changesets on code hosts. Some changesets may be unmergeable due to their states, which does not impact the overall bulk operation. Failed merges are listed under the bulk operations tab. In the confirmation modal, you can opt for a squash merge strategy, available on GitHub, GitLab, and Bitbucket Cloud. For Bitbucket Server/Data Center, only regular merges are performed |
+| **Merge** | Merge the selected changesets on code hosts. Some changesets may be unmergeable due to their states, which does not impact the overall bulk operation. Failed merges are listed under the bulk operations tab. In the confirmation modal, you can opt for a squash merge strategy, available on GitHub, GitLab, and Bitbucket Cloud. For Bitbucket Server/Data Center, only regular merges are performed |
 | **Close**                | Close the selected changesets on the code hosts                                                                                                                                                                                                                                                                                                                                                          |
 | **Publish**              | Publishes the selected changesets, provided they don't have a [`published` field](/batch-changes/batch-spec-yaml-reference#changesettemplatepublished) in the batch spec. You can choose between draft and normal changesets in the confirmation modal                                                                                                                                       |
 | **Export**              |  Export selected changesets that you can use for later use                                                                                                                                       |
 | **Re-execute**              |  Users can re-execute individual changeset creation logic for selected workspaces. This allows for creating new changesets for users who are using non-deterministic run steps (for example,LLMs)                                                                                                                                       |
+| **Enable auto-merge for GitHub (experimental)** | Enable auto-merge on selected GitHub changesets. When enabled, changesets will be automatically merged once all required status checks pass and any blocking reviews are resolved. This feature is GitHub-specific and requires [appropriate setup](https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-auto-merge-for-pull-requests-in-your-repository) on the target repositories. Failed actions are listed under the bulk operations tab. |
 
 ## Monitoring bulk operations