Deploy swh.loader.core v3.0 (and other impacted loaders)

loader.core v3.0 and impacted packages (loader.cvs, loader.svn, loader.git, loader.mercurial, ...).

Plan (staging, then production):

• Deploy loader.{core,cvs,git,svn,bzr,mercurial}.
• Restart impacted services swh-worker@loader_{vcs} for vcs in ...
• Might as well restart the machines directly...

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Migrated from T4189 (view on Phabricator)