Deprecate Praefect's reconcile sub-command

What does this MR do?

This MR deprecates Praefect's reconcile sub-command as it is no longer needed.

Praefect's reconcile sub-command was historically the only way to reconcile repositories between the Gitaly storages in the cluster. Since then, Praefect has gained an automatic reconciler. The automatic reconciler has multiple benefits compared to the manual one:

1. It's automatic and needs no intervention from the administrator.
2. The automatic reconcile takes more considerations, including not scheduling redundant jobs, making sure the source replica of a job is not pending deletion.
3. The manual reconciler does not adjust for repository-specific primary nodes nor for variable replication factor. It will mirror a whole storage always, which makes it inflexible.
4. The automatic reconciler performs better due to walking database records rather than the repositories on the disk.

Given the above, these days there's no reason to run the manual reconciler. Any replication jobs it schedules that the automatic reconciler would not schedule are dropped by Praefect due to various checks like downgrade protection. Let's deprecate the reconcile sub-command in 13.12 as it is no longer needed.

Related issues

gitaly#3574 (closed)

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