Document setting up `client_credentials` with access tokens scoped to the application

[sjohnr]

We should add a clear example to the reference for setting up an application with the client_credentials grant type. Often, this use case requires access tokens scoped to the application instead of individual users in session.

Related gh-15295

[FryingHellfish]

Hi @sjohnr,

Would you be kind enough to share some code snippets related to this example, specifically for reactive applications? We're encountering similar issues as described in gh-10083 and gh-13816, and we're very interested in finding a solution.

Thank you in advance.