Issue transition hooks should only apply on repo's main branch (BB-9461)

Suppose I push a fix to a bug on a branch called "bugfix-123" and in my commit message I write "Blah, fixes BCLOUD-123".

In my opinion the issue is not resolved until it's in the main branch. It should not close the issue until my pull request has been merged.

The current behaviour is that the issue gets changed to resolved. If my branch never gets merged (pull request rejected, for example) the issue has not been resolved.

Furthermore I think it's particularly misleading for an observer of the repository to see issues set to resolved when they are in fact not resolved in the master branch.