Coordinated pipeline stages

This is at the proof-of-concept stage, but aims to implement the second step of gitlab-com/gl-infra&201 (closed), where a tagged release-tools pipeline will tag and then wait on the Omnibus and CNG builds.

This MR reorganizes our CI configuration's pipeline stages:

1. deploy gets renamed to coverage to avoid confusion with a future deployer stage
2. Adds coordinated:tag, :build, and :deploy stages which are hopefully self-explanatory
3. Adds a .coordinated-pipeline template for use by jobs in those new stages, enforcing that these jobs only run on tagged release-tools pipelines.

TODO

1. Remove the CI_COMMIT_BRANCH check, used for debugging only
2. Remove the only: refs: branches rule, used for debugging only
3. Re-implement the auto_deploy:start job
4. Increase the delayed job time

Implementations for auto_deploy:builder:omnibus and :cng will be in a future MR.