Disallow disabling auth extensions while being used by settings sync

[sandy081]

Currently one can disable an auth extension that provides auth token for settings sync.

We shall disallow this.

[sandy081]

@RMacfarlane This needs extension declaring auth providers through package.json. By doing so, we can detect if an extension is contributing an auth provider and check if those auth providers are being used for settings sync or not and prevent it from disabling.

This also helps settings sync to have deterministic initialisation - wait until providers are registered and initialise.

[sandy081]

@RMacfarlane Is there a request to track static contributions for authentication providers?

[RMacfarlane]

Yeah, here's the issue for it: #103507

[sandy081]

To verify:

• Make sure you can disable auth provider extensions (Github/Microsoft) can be disabled only globally.
• Disabling these extensions at workspace level is not allowed
• If Settings Sync is on and using one of these accounts, Make sure you cannot disable that extension at all.