Setup staging infrastructure

Setup such infrastructure to allow testing:

• puppet changes before pushing git commits to the forge
• deployment (through puppet)
• deployed modules are running as expected
• for external clients (deposit e.g. hal, vault, etc...)

Draft pad available at [1]

• [1] https://mensuel.framapad.org/p/swh-staging-area

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Migrated from T1785 (view on Phabricator)