batches: Add query to determine available bulk operations

Created by: BolajiOlajide

Description

This pull request moves the logic of determining what Bulk Operations apply to a number of selected changesets to the backend.

Test plan

1. Navigate to a batch change page. Example https://sourcegraph.test:3443/users/bolaji/batch-changes/all-drafts-all-the-time?visible=2.
2. Ensure the batch change contains a number of changesets.
3. Select a number of changesets, and the bulk operation option should be shown
4. The option displayed should match bulk operations that can be performed on the selected changesets depending on their statuses.

Logic Breakdown

• Changesets belonging to an archived batch change have the following bulk operations available:

  • COMMENT
  • DETACH

• Changesets with a FAILED reconciler state have the following bulk operations available:

  • REENQUEUE

• Changesets in an UNPUBLISHED state have the following bulk operations available:

  • PUBLISH

• Changesets in a DRAFT state have the following bulk operations available:

  • COMMENT
  • CLOSE
  • PUBLISH

• Changesets that are in an OPEN state have the following bulk operations available:

  • COMMENT
  • CLOSE
  • PUBLISH
  • MERGE

• Changesets in a CLOSED state have the following bulk operations available:

  • COMMENT

• MERGED changesets have the following bulk operations available

  • COMMENT
  • CLOSE

Closes #21185

App preview:

• Link