feat: Add PKCE Verifier for OIDC

[Rorical]

From PR #1812 :

To fix the error "Could not exchange code for the token" when using the PKCE method, a verifier should be generated and used during the authentication process.

This change include change in configuration, oidc handling method and documents.

oidc:
  # Optional: PKCE (Proof Key for Code Exchange) configuration
  # PKCE adds an additional layer of security to the OAuth 2.0 authorization code flow
  # by preventing authorization code interception attacks
  # See https://datatracker.ietf.org/doc/html/rfc7636
  pkce:
    # Enable or disable PKCE support (default: false)
    enabled: false
    # PKCE method to use:
    # - plain: Use plain code verifier
    # - S256: Use SHA256 hashed code verifier (default, recommended)
    method: S256

[kradalby]

Great, I'm off the computer for a few days, could you push the draft as discussed and try to write up an issue for the proxy for later while it is fresh in memory?

[kradalby]

Could you also add a changelog line?

[Rorical]

Sure, draft is at #2315

[Rorical]

Should this be done in v0.24.0 or Next?

[Rorical]

Should this be done in v0.24.0 or Next?

I mean where should I write this change in changelog

[kradalby]

0.24 is good