feat(dcr): Add Redis storage support for multi-replica deployments (#109)

- [x] Add file and Redis storage backends for DCR credentials
- [x] Implement storage abstraction with FileStore and RedisStore
- [x] Add factory function for automatic backend selection (auto/file/redis)
- [x] Integrate DCR credentials cache into UniversalCacheManager
- [x] Add comprehensive tests for storage backends and factory
- [x] Update configuration schema with storage backend options
- [x] Update documentation with multi-replica deployment guidance
- [x] Add Redis key prefix configuration for credential isolation

README.md

@@ -8,7 +8,7 @@ The Traefik OIDC middleware provides a complete OIDC authentication solution wit
 
 - **Universal provider support**: Works with 9+ OIDC providers including Google, Azure AD, Auth0, Okta, Keycloak, AWS Cognito, GitLab, and more
 - **Automatic provider detection**: Automatically detects and configures provider-specific settings
-- **Dynamic Client Registration (RFC 7591)**: Automatic client registration with OIDC providers without manual pre-registration
+- **Dynamic Client Registration (RFC 7591)**: Automatic client registration with OIDC providers without manual pre-registration, with Redis storage support for multi-replica deployments
 - **Automatic scope filtering**: Intelligently filters OAuth scopes based on provider capabilities declared in OIDC discovery documents, preventing authentication failures with unsupported scopes
 - **Security headers**: Comprehensive security headers with CORS, CSP, HSTS, and custom profiles
 - **Domain restrictions**: Limit access to specific email domains or individual users