gRPC to REST/OpenAPI based services

[jelmansouri]

Summary

• Expose backend APIs that are accessible by all the different client types, standalone and web clients.
• Use a rust framework/crate that can ideally provide the following components:
  • Code generation for both service and client based on an API contract.
  • Easy to use and feature rich.
  • Support for async/await.
  • Compatible with our tokio runtime stack.
  • Potentially based on the HTTP client hyper we already use.
  • Ideally low amount of dependencies.

Current State

PROS

• Provides Rust code generation.
• Performant gRPC protocol based on protobuf (binary message format).

CONS

• Different protocols for web (grpc-web on HTTP/1.1 & 2) and standalone clients (HTTP/2) (need two load balancers).
• Rust gRPC implementation tonic is powerful but complex.

Tasks

• [x] #1526
• [x] #1529
• [ ] #1525