Add Build Trigger to Only Check HEAD Commit of Pull Requests

Currently, commit_message applies regex for all of the commits in a pull request history
Please add an option for build triggers that only evaluates the HEAD commit of a pull request.

For example, this feature could be useful if we want to trigger a build only when the latest commit in the PR is made by a human and not by bots, which often add automated commits (e.g., dependency updates, linting fixes, build version updates and etc.)