Launchpad MP (500665) - r00ta/openfga-permission-layer

[r00tabot]

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Commit message: feat: replace built-in permission layer with openfga.
Details:

• introduce a sync/async client to interact with openfga
• introduce a context cache in maasserver: when a new websocket/http request is processed, all the calls to openfga are cached so to avoid hammering the server.
• migrate existing users to the pre-defined groups users/administrators.
• grant a set of default permissions to users/administrators groups so to guarantee backwards compatibility.
• Introduce a new check_permission decorator so to simplify the permission checks on openfga
• minor changes to the openfga model, so to have feature parity with RBAC.