feat: implement OIDC provider management and discovery features

- Introduced OIDC provider management capabilities, including registration, retrieval, updating, and deletion of providers.
- Added support for OIDC discovery, allowing dynamic fetching of provider configurations from `.well-known/openid-configuration` endpoints.
- Created domain entities for OIDC configuration, including `ClaimMapping`, `OidcProviderConfig`, and presets for common identity providers.
- Implemented gRPC endpoints for OIDC provider management and discovery operations.
- Enhanced tests for OIDC domain entities and gRPC mixins to ensure comprehensive coverage.

All quality checks pass.

pyproject.toml

@@ -207,6 +207,7 @@ dev = [
     "basedpyright>=1.36.1",
     "pyrefly>=0.46.1",
     "pytest-benchmark>=5.2.3",
+    "pytest-httpx>=0.36.0",
     "ruff>=0.14.9",
     "watchfiles>=1.1.1",
 ]