Geo: Do not attempt to verify/replicate Git repo when project_repositories (and Git repo) doesn't exist

This is part of a multi-step implementation plan to handle Geo verification/replication of projects without Git repositories to reduce errors caused when Gitaly tries to fetch non-existent repos.

	Steps
1	Add had_repo column in <repo type>_repositories table
2	Backfill has_repo column
3	Introduce a feature flag to be used in the next two steps
4	Insert record in <repo type>_repositories only when a Git repo is created; at the same time update has_repo
5	Enumerate <repo_type>_repositories instead of repo types table for verification/replication of Git repos, if not already done
6	Do not attempt to verify/replicate Git repo when <repo type>__repositories (and Git repo) doesn't exist	👈 You are here
7	Delete project_repositories rows where Git repos don't exist

Once project_repositories records and project.has_repo column are consistent with the existence of a project's Git repo, we want Geo code to verify/replicate Git repos only when they exist.