Expand OSC docs for token usage

[osfrickler]

In docs/guides/other-guides/testbed.mdx the chapter OpenStack CLI token issue with OpenID Connect describes how to generate a token.

Add some information about how to use this token.

[ideaship]

This issue looks stale. The referenced information has been removed from the repo some time ago.

[jklare]

Agreed. I think this is also something that we can address in the context of KeyCloak.