Fix an error where we were unable to create a CommitStatus for running state

What does this MR do?

Due to severe refactoring of Pipeline we introduced regression in how CommitStatus is handled. We received an report that it's impossible to create a CommitStatus with state running when there were not previous status.

Are there points in the code the reviewer needs to double check?

The support for Commit Statuses should be simplified. Right now I'm doing minimal change to move forward and fix a bug, but I'll create a new MR that will move all logic that is now part of lib/api/commit_statuses.rb to separate service to simplify the implementation.

Why was this MR needed?

This error happens due to the fact that we introduced additional status of builds: created.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/21345