Simplify CI/CD configuration on serverless projects

What does this MR do?

This merge request introduced CI/CD template that one can use to simplify deployment of functions / apps in their serverless projects.

What are the relevant issue numbers?

Closes gitlab-org/gitlab-ce#57405

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Conforms to the code review guidelines
• Security reports checked/validated by reviewer