Add sync-l10n command for l10nupdate

Summary:
Add a new sync-l10n command that can be used to copy the l10n files for
a deployed MediaWiki version to the cluster and then trigger a rebuild
of the l10n cache files for the same version. This will be used by the
nightly l10nupdate process to replace its current use of sync-dir
followed by scap-rebuild-cdbs using dsh.

Test Plan:
Beta cluster doesn't have l10nupdate jobs setup, but it should be
possible to just run this new command manually.

Reviewers: Release-Engineering-Team, demon, mmodell, thcipriani, dduvall, ori

Reviewed By: ori

Subscribers: Krenair, Reedy

Maniphest Tasks: T72443

Differential Revision: https://phabricator.wikimedia.org/D65