Start implementing the grpc

Signed-off-by: Nikolai Rodionov <allanger@badhouseplants.net>

lib/proto/audio_backend.proto

@@ -1,6 +1,23 @@
 syntax = "proto3";
 package termix.audio_backend;
 
-service AudioBackend {
+import "google/protobuf/empty.proto";
 
+service AudioBackend {
+  rpc StartClient(google.protobuf.Empty) returns (google.protobuf.Empty);
+  rpc InitConnection(google.protobuf.Empty) returns (google.protobuf.Empty);
+}
+
+message Shirt {
+    // Label sizes
+    enum Size {
+        SMALL = 0;
+        MEDIUM = 1;
+        LARGE = 2;
+    }
+
+    // The base color
+    string color = 1;
+    // The size as stated on the label
+    Size size = 2;
 }