Add commitlint template

Add a template to run commitlint against commits. As teams start to follow the Conventional Commit spec it would be nice to have the option of linting commit messages in CI. This becomes more important as we start to build automation around the commit messages, requiring them to adhere to this spec rather than just being a ideal.

NOTE: The ideal place for commit lint to run is in a pre-commit hook, however, as lots of teams are still new to pre-commit it is beneficial to also have a template to add a job to the CI pipelines.