Create pending status check responses on MR creation

The following discussion from !120903 (closed) should be addressed:

• @jmontal started a discussion: (+3 comments)

  But... I've run into an issue though as I've forgotten that status check responses are not created when an MR is initially created, thus this worker has nothing to update as the response does not exist yet so I'll hold back on asking you to review until I can figure out a solution

!113926 (comment 1311751145)