Implements Proof Key for Code Exchange for OpenID Connect Authorization Code Flow. By default this is enabled for the public client type and requires the S256 challenge method.
Closes#2921
This implements the public option for clients which allows using Authelia as an OpenID Connect Provider for cli applications and SPA's where the client secret cannot be considered secure.
This is a required endpoint for OIDC and is one we missed in our initial implementation. Also adds some rudamentary documentaiton about the implemented endpoints.
* This gives admins more control over their OIDC installation exposing options that had defaults before. Things like lifespans for authorize codes, access tokens, id tokens, refresh tokens, a option to enable the debug client messages, minimum parameter entropy. It also allows admins to configure the response modes.
* Additionally this records specific values about a users session indicating when they performed a specific authz factor so this is represented in the token accurately.
* Lastly we also implemented a OIDC key manager which calculates the kid for jwk's using the SHA1 digest instead of being static, or more specifically the first 7 chars. As per https://datatracker.ietf.org/doc/html/draft-ietf-jose-json-web-key#section-8.1.1 the kid should not exceed 8 chars. While it's allowed to exceed 8 chars, it must only be done so with a compelling reason, which we do not have.
