Standardized usage for Envoy Gateway

[Xunzhuo]

Currently we use EnvoyProxy CR to manually patch the boostrap to add external processing filter, add original_destination_cluster for envoyproxy. This is not a recommended approach to use eg and gateway api, and this is very static and hard to maintain, and breaks the design of gateway-api concepts.

We should standardize to use eg and gateway api by:

1. Use EnvoyExtensionPolicy CRD to dynamically set up external processing filter for gateway listener.
2. Use EnvoyPatchPolicy CRD or implement extension hook server to add original_destination_cluster.
3. Remove envoyproxy CRD, to prevent manually patching the bootstrap.

/assign

[smarterclayton]

/assign @kfswain