remove-repository: A new sub-command for the praefect to remove repository

Users of the praefect are missing tools to manage state of the cluster. One of such tools is a repository removal cli. It should be used to remove any repository from the cluster. The removal covers cleanup of the database and removal from the gitaly storages. The command tries to remove as much as possible first by removing from praefect, replication event queue and each gitaly node configured in the provided config file.

Part of: #3771 (closed) & #3769 (closed)