feat: add gitlab service

[aslafy-z]

Fixes https://github.com/argoproj/notifications-engine/issues/137

TODO:

• Add tests for repo name to PID compute
• Figure out how to reuse existing deployments (Do something like https://github.com/argoproj/notifications-engine/pull/235?)
• Option: Assumption: The referenced Environment is managed by ArgoCD notifications. Any updates will create a new deployment res.
• Add option to delete that stop the environment.
• Find the max length for commit statuses descriptions
• Write documentation
• Reduce code for templated fields (like https://github.com/argoproj/notifications-engine/pull/223?)