e2e test mock provider unification #13041
Description
- Our remote jwt fetch e2e tests are currently using this mock provider: https://github.com/kgateway-dev/kgateway/tree/main/hack/dummy-idp
- The authn mcp tests require the oauth 2.0 flow so they're using a different mock provider based on the agw example: https://github.com/kgateway-dev/kgateway/tree/main/hack/dummy-auth0
- envoy OIDC are planning to use keycloak
Unify the e2e tests to use one provider (maybe keycloak, then group the keycloak-dependent tests).