Implement ADR 0026 - making keystone oauth2 OP #939

The ADR 0026 describes how to make the keystone a oauth2 OP.

Phase 1: Cryptographic Engine & JWKS Infrastructure
Phase 2: Ingress API Routing & OIDC Discovery
Phase 3: Machine-to-Machine client_credentials Implementation
Phase 4: Human Authorization Code Flow with PKCE
Phase 5: Native Control Plane Acceptance & Middleware Injection

This is the umbrella issue tracking the status