Better CI integration: Add a build status API for commits (BB-9631)

Hi,
It would be nice if Bitbucket supported one of Stash's features, which also GitHub has it, build status api for commits as described here: https://developer.atlassian.com/stash/docs/latest/how-tos/updating-build-status-for-commits.html

With this API, we could better integrate BitBucket with our current CI server.