AIP-79 Register endpoints from auth manager into FastAPI

[jason810496]

closes: #44882

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[pierrejeambrun]

This cannot be done yet.

The ticket depends on #44847 (cf issue description), which will update the provider interface and allow us to retrieve a new fastapi router to register extra routes coming from the provider.

We don't want to embed the flask legacy code into the new fastapi (That's only true for supporting legacy v2 plugins), but for the rest we want to convert them to fastapi. (convert the legacy routes to fastapi routes, expose a native fastapi router, and register that).

I think we will have to wait a little bit :)

[jason810496]

Thanks for the reminder! I’ll wait until #44847 is resolved.