make sure front-end services work when the Inria infra is down

During the last planned downtime it has become evident that front-end services (like the web app) does not work when the infrastructure hosted at Inria is down, in spite of being (at least in theory) fully cloud-hosted.

We should evaluate why that has been the case and make front-end services really independent from services currently running at Inria.

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Migrated from T1843 (view on Phabricator)