docs: add mcp fallback auth flow with client credentials

[wagnerjt]

Supports #252892

[wagnerjt]

@microsoft-github-policy-service agree

[wagnerjt]

@TylerLeonhardt :)

[ntrogh]

@TylerLeonhardt can you do a quick review?

@wagnerjt Thanks for updating the docs! I'll do a final pass after Tyler's review. Also, given this will land in Stable (1.103) next week, I'll hold off on merging until we release.

[TylerLeonhardt]

Besides the one comment I think this looks good. Thanks for contributing!

[TylerLeonhardt]

@ntrogh I defer to you for a edit pass :)

[ntrogh]

@wagnerjt Completed my edit pass, just a couple of minor edits. Appreciate you updating the docs!

[ntrogh]

@wagnerjt Thanks for the updates. As mentioned, will hold off on merging until we release.

[wagnerjt]

@wagnerjt Thanks for the updates. As mentioned, will hold off on merging until we release.

Thanks for the feedback and makes sense. I'll leave it in your hands :)