Flag multi-branch commits in the REST API

When a commit has multiple parents, all of these parents are sent through the REST API when the Jira development panel requests them. Multiple parents flag a merge commit in that development panel. However, there is a case where a commit exists in multiple branches, so it has multiple parents. Though this would not be a merge commit, anything relying on multiple parents signifying a merge would have incorrect information.

Either only one parent should be sent in these situations, or a flag should be sent along with the commits indicating this is not a merge. The Jira development panel would then need to honor this flag.

https://getsupport.atlassian.com/browse/PS-46999