Description of metadata related pods and services

[gtarcoder]

/kind feature

Describe the solution you'd like [A clear and concise description of what you want to happen.] There are many .. pods and servcices in kubeflow related with metadata: Pods: metadata-db-xx metadata-deployment-xxx metadata-envoy-deployment-xxx metadata-grpc-deployment-xxx metadata-ui-xxx

Services: metadata-db metadata-envoy-service metadata-grpc-service metadata-service metadata-ui

Anything else you would like to add: [Miscellaneous information that will assist in solving the issue.] Could you help to describe :

1. what are these pods and services, what do they do. which urls those serivces serve.
2. Relationship between each other of those pods and serivces.
3. What are the dockerfiles of those pods
4. Where is the source repo and directory of each service.
5. according to this page https://www.kubeflow.org/docs/components/metadata/, the Kubeflow metadata deploys the gRPC service of ML Metadata (MLMD) to manage the metadata and relationships. So what's the relationship between ml-metadata-grpc service(source https://github.com/google/ml-metadata) and the metadata service (source https://github.com/kubeflow/metadata/blob/master/server/main.go), does the latter call the former? Or they are the same thing?

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