Add an option to "Require commits to be associated with a JIRA issue" to only check commit messages (not branch name)

The "Require commits to be associated with a JIRA issue" Script Pre Hook currently allows a commit if either the commit message or the branch name has a JIRA issue. However, for pull request workflows this isn't very useful because the branch will always have an issue key in the name but the branches are short lived. What we really need is to ensure that every commit that gets merged into master has a JIRA issue key in the commit message.

It makes sense to also add this option to the "Require Pull Request to be associated with a JIRA issue" Script Merge Check.