Add a new deployment job for the "ring-0"

What does this MR do and why?

This MR introduces the Ring 0 deployment into our coordinate pipeline.

Key concepts:

• the deployment is managed in a child pipeline so that we can apply resource_group locking at the whole process
• the deployment is managed by an environment feature flag. Setting $FF_RING0 will enable that feature
• the child pipeline commits an updated tenant model to cells-tissue with SKIP-CI in the commit message and then triggers a pipeline to start the deployment

An old example deployment (on switchboard_uat) can be seen in https://gitlab.com/gitlab-org/release-tools/-/pipelines/1170982958, that was triggered by this MR.