Feat/support claim matching based on login hint

[d-lopes]

This PR adds support for matching token callback mappings against original authorization request parameters such as login_hint and other extra auth request args.

Why is it useful?
This improves the server’s ability to drive token issuance based on the original OIDC auth request, while keeping existing token callback behavior unchanged for non-auth-code flows.

How it works? / What is changed?
The Authorization code flow now preserves auth request query parameters and merges them into token callback matching. The RequestMappingTokenCallback can match on auth request params like login_hint, acr_values, claims, or any custom extra parameter.
The Auth request params can also be used in claim templates, e.g. \"email\": \"${login_hint}\".

In addition, README.md was updated to document the new behavior and provide examples for login_hint-based matching.

[d-lopes]

I realised that there are still docker build related settings here that point to my repo where I forked your mock-oauth2-server.

I am not sure how to isolate it in a way where these details do not end up in your repo but keep the docker build working for me :/