Add support for key/signature based authentication to gRPC about frequenz-api-dispatch HOT 2 OPEN

syntax = "proto3";

package example;

// The MyService provides an API for managing various resources.
// ALL requests to this service must be signed. The key and signature 
// should be added to the request metadata (HTTP headers). The signature 
// should be computed using the HMAC-SHA256 algorithm and the user's secret key.
service MyService {
    ...
}