This change:
- Allows checking "Squash commits" in MRs with 1 commit for
  projects with allowed/encouraged squash.
- Performs squash when merging MR for projects with enforced
  squash in MRs with 1 commit.
- Skips performing squash only when there's 1 commit in MR and
  squash commit message is the same as existing commit message.
  When no message is passed, it's compared to default squash
  commit message.

Changelog: changed