Condition feature flag toggle to running sync-metadata

[FelixMalfait]

With the new admin panel it's easy to toggle a feature flag like "Workflows" which require a sync-metadata and set your workspace in a corrupted space. I assume this will generate a lot of support.

We should introduce a way to restrict some toggle or maybe have something more intelligent to be able to track if it can be turned on safely.

In the future we want to be able to run sync-metadata directly from the admin panel with a button, maybe that's the right path?

[Bonapara]

Does disabling a feature flag reset things, or is it irreversible?

1. Before I run sync-metadata?
2. After I ran sync-metadata?

[FelixMalfait]

We should introduce isPublic on featureFlags (public flags can be changed by users on the cloud or self-hosting, it's a pre-release mode ; default to False). We'll have a new dedicated page for public featureFlags.

We'll keep the admin panel for non-public feature flags but only display it on our cloud version, for ourselves. We don't want to display it by default to self-hosters. We can rely on IS_BILLING_ENABLED or DEBUG_MODE as a proxy for those.