Migrate content store service

[tltran-legion]

Summary

Goal is to migrate the Content Store service to OpenAPI using the Code Generation framework.

Current State

At the moment, the Content Store service is using gRPC we need it to follow the defined new API convention.

Work Items

• [x] Using the Code Generation Framework to generate the service skeleton.
• [x] Port of the actual business logic of the service into the new skeleton.
• [x] Improve the generated codegen client to support authentication.
• [x] Reuse the common types from the API with the governance service.

[tltran-legion]

https://github.com/legion-labs/legion/pull/1982