Implement xDS APIs

[mostafa]

Integrate with xDS APIs via streaming gRPC to give control-planes the ability to talk with GatewayD.

Resources

• https://github.com/grpc/test-infra/tree/master/containers/runtime/xds-server (fake xDS server for testing) ⭐
• https://github.com/ii/xds-test-harness
  • https://github.com/greymatter-io/xds-test-harness ⭐
• https://github.com/getsentry/xds ⭐
• https://github.com/wongnai/xds
• https://github.com/cncf/xds
• https://github.com/grpc/grpc/tree/master/examples/python/xds
• https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/operations/dynamic_configuration
• https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol
• https://www.envoyproxy.io/docs/envoy/latest/api-v3/api
• https://pkg.go.dev/google.golang.org/grpc/examples/features/xds
• https://github.com/getsentry/xds
• https://medium.com/@rajithacharith/introduction-to-envoys-dynamic-resource-discovery-xds-protocol-d340032a63b4
• https://cloud.google.com/traffic-director/docs/xds-control-plane-apis
• https://www.cloudwego.io/docs/kitex/tutorials/advanced-feature/xds/