Support Envoy AI gateway v0.2.0

<!-- Please only use this template for submitting clean up requests --> **What would you like to be cleaned**: Envoy AI Gateway just released v0.2.0 days ago, which supports some features like customized ownedBy, created which is helpful to our project. Also, it no longer supports service directly but the backends, which will impact our envoy ai gateway example in `docs/examples/envoy-ai-gateway`, basically, we should replace the service with the backend. See release note: https://aigateway.envoyproxy.io/release-notes/v0.2#%EF%B8%8F-breaking-changes **Why is this needed**: