Make Hashed Storage a hard requirement of GitLab Geo

Hashed Storage solves all sorts of problems and race conditions for Geo.

In https://gitlab.com/gitlab-org/gitlab-ce/issues/40970, we concluded that Geo needs Hashed Storage. The issue is closed because the goal was to create a plan.

Now that Hashed Storage is out of beta, we should make it a requirement of Geo.

• Modify the Legacy Storage + Geo paragraph to be a warning, and say it is unsupported since Hashed Storage is requirement. Repository Storage Types | GitLab
• Make Hashed Storage non-optional Geo configuration (GitLab Omnibus) | GitLab
• Make Hashed Storage non-optional Geo configuration (source) | GitLab