actix-prost: Support nested messages in query

[bragov4ik]

It might be useful to have nested/complex messages, parts of which are specified in query.

prost-build seems to work with them well (the rust code is generated accordingly). However, actix-prost fails with

thread 'main' panicked at actix-prost-build/src/request.rs:75:13:
  some path fields were not found: [<field names>]

Example

Let's say we have the following protobuf:

...
message Foo {
  // some_scary_inner_details
  string inner = 1;
}

message Bar {
  // some_scary_inner_details
  string inner = 1;
}

message CreateSometingRequest {
  Foo foo = 1;
  Bar bar = 2;
}

service SomeService {
    rpc CreateSomething(CreateSometingRequest) returns (Something);
}

so the request message has 2 non-primitive fields.

The .yaml config:

...
http:
  rules:
  - selector: "foo.SomeService.CreateSomething"
    post: /service/{foo.inner}/{bar.inner}

Possible fix directions

seems relevant; not sure

• https://github.com/grpc-ecosystem/grpc-gateway/blob/d97fdab937cf9bb946fd7a3a0bca59bc7389d127/protoc-gen-openapiv2/internal/genopenapi/template.go#L267