Modifying the commit message using change edits needs two separate API
calls:
PUT /changes/{change-id}/edit:message
POST /changes/{change-id}/edit:publish
Since it requires two API calls, the operation is not atomic and can
leave a user with an unpublished edit.
PolyGerrit wants to support editing a commit message as an atomic
operation even before support for change edits is built.
This commit adds a new API endpoint on the change resource that
allows to edit the commit message of a change atomically.
It does not reuse the code from a previous implementation since the
underlying infrastructure changed and we now use BatchUpdate.
Bug: Issue 6502
Change-Id: I60595df074b00a503165c41485b69a5fe0c5de39
fda9645d2f