Clarify gRPC and Amino

[moul]

I believe it's time to clarify the targets of this repository in relation to gRPC and amino.

Context

• Amino is compatible with some gRPC features, providing more limited functionality, which we currently embrace internally.
• Using amino allows independence from gRPC and protobuf stack, reducing reliance on external tools and services.
• While protobuf is not prohibited, it could be encouraged outside the main repository, especially in clients, alongside amino for those using languages like Go.

Proposals

• Update Amino's README with current information and provide clearer details on the goals and non-goals.
• The main repository should solely rely on amino as the protocol, simplifying dependencies to just "go" for building, testing, and publishing. Clearly state it and the constraints in CONTRIBUTING.md.
• Automate .proto file generation through CI for easier access. Centralize these files in a dedicated folder in the main repo or a separate repo. Set up dedicated repositories for each supported languages using protoc-gen- to streamline new releases and enable extending generated clients with extra helpers. I suggest planning this and postponing it for later, except for the .proto generation part.
• Create a documentation page on "interacting with the gRPC API as a client," linking to practical examples like those from @gnolang/berty, cc @jefft0 @D4ryl00 @iuricmp @costinberty. Add a documentation section on how to interact with the chain without using Gnoweb or Gnokey #2026

Related to issue #620