xDS protocol for service discorvery

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https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol

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• Proposals: https://github.com/grpc/grpc/blob/master/doc/grpc_xds_features.md
  • https://github.com/grpc/proposal/blob/master/A27-xds-global-load-balancing.md
  • https://github.com/grpc/proposal/blob/b44e768b0cd542c489ef4b9ca6741aa78f019100/A36-xds-for-servers.md
  • https://github.com/grpc/proposal/blob/deaf1bcf248d1e48e83c470b00930cbd363fab6d/A29-xds-tls-security.md
  • https://github.com/grpc/proposal/blob/28dfdf6145fbebc715a36c25ca5631c5e24944c1/A41-xds-rbac.md
• Interop: https://github.com/grpc/grpc-go/blob/v1.39.0/interop/xds/server/server.go
• Example: https://github.com/grpc/grpc-go/blob/master/examples/features/xds/server/main.go