feat: add gitlab service

[aslafy-z]

Fixes #137

TODO:

• Add tests for repo name to PID compute
• Figure out how to reuse existing deployments (Do something like github: reuse existing deployment when sending new notification #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 feat(github): Add checkrun support #223?)