WIP: Triggermesh phase1 - Knative support

Initial phase introducing Knative Support to GitLab Projects

Add support for Knative by adding a Kubernetes cluster application, and necessary hooks to deploy the service from the CI/CD pipeline into the list of functions.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides