Implement gRPC service

[oubiwann]

Preparation:

• Add ASCII support (see Add new ASCII output option #6)
• Update current CLI usage (see Update the Rust app to produce images for cave features #5)
• Define service features (see Define feature set for noise service #7)
  Dev tasks:
• Create protobuf protocols that match features defined in Define feature set for noise service #7
• Restructure app to follow the example given in Consider running a gRPC service #2:
  • Update Cargo.toml for gRPC
  • Add builder
  • Add server impl

[oubiwann]

See this comment for an example:

• Consider running a gRPC service #2 (comment)