[Research Spike] Research if it's possible to deprecate environment refs advertisement

Problem

GitLab has a feature to advertise environment git-refs for allowing users to fetch specific version of code. This ref is created for each environment with a format refs/environments/<env-name>/deployments/<iid>.

As stated in #296625 (closed) and #19724 (closed), if a project uses Review Apps, a new environment is created for each feature branch, which results in tons of environment refs exist in one repository and slows down the git-fetch. This is a ~performance issue.

Technically, users don't need to use this ref, as they can simply fetch the deployment SHA directly. So I wonder if we can terminate the feature to speed up git-fetch performance.

Proposal

We should investigate how many users are actually fetching the environment refs and if it turned out it's very low usage, we should consider deprecate it (and eventually remove).

If we conclude that this ref doesn't need to be advertised, we can add hideRefs config to the Omnibus GitLab. Example

Since this is breaking change, the change must happen at a major version update e.g. 14.0. We also should make a pre-announcement to give heads up to users.