feat(openid-connect): add stateless session revocation options

[Hockenba]

Summary

• Add session.redis.mode (storage | revocation) and session.revocation_fail_mode (open | closed) to the openid-connect plugin schema.
• Pass session configuration through to lua-resty-session as-is; revocation is auto-loaded by the library when storage is cookie and Redis is configured for revocation (no APISIX-side revocation=true translation).
• Add t/plugin/openid-connect-revocation.t covering schema validation, config passthrough, and fail-open/fail-closed runtime behavior.

Dependency

This plugin change depends on lua-resty-session cookie-session revocation support (Redis denylist on open() / destroy()). A companion change PR is required in
lua-resty-session before this can land in APISIX.

Test plan

• prove t/plugin/openid-connect-revocation.t (with lua-resty-session revocation support installed)
• prove t/plugin/openid-connect*.t
• Verify cookie-session logout invalidates sessions when session.redis.mode is revocation
• Verify revocation_fail_mode=open allows requests when Redis is unreachable
• Verify revocation_fail_mode=closed rejects sessions when Redis is unreachable