Minimize duplication in OIDC Bearer and Code flow docs

[sberyozkin]

Description

OIDC bearer and code flow reference docs start with some flow specific content and then cover the material which is relevant to both flows, such the discovery, userinfo, token access.

Sometimes one of these docs links to another one and it can become very confusing.

Implementation ideas

Even though there is some shared content, moving it all into a dedicated doc to be referenced from both OIDC bearer and code flow docs may not work as each each flow has some nuances or specifics. For example, when dealing the bearer tokens, it is irrelevant how the OIDC token endpoint can be discovered since the OIDC token acquisition only works during the code flow, etc.

It looks like, the simplest approach is to do the clean duplication, avoiding each of the docs linking to some parts of the other docs. For example, currently, OIDC bearer doc section on the OIDC request filters links to the the relevant section in the OIDC code flow doc - forcing users to switch focus to another, more complex code flow reference doc, even though they may not be interested in it

[quarkus-bot]

/cc @pedroigor (bearer-token,oidc)