Set proper User-Agent on native iOS/Android API requests

Native gRPC-web API calls previously went out with the generic
CFNetwork/Darwin (iOS) user agent. Add a metadata interceptor that
sets a recognisable CouchersNative User-Agent on every request.

Co-authored-by: Aapeli <aapeliv@users.noreply.github.com>

Author: github-actions[bot]

app/mobile/service/client.ts

@@ -3,6 +3,7 @@ import { AuthPromiseClient } from "@/proto/auth_grpc_web_pb";
 import { NotificationsPromiseClient } from "@/proto/notifications_grpc_web_pb";
 
 import isGrpcError from "@/service/utils/isGrpcError";
+import { applicationNameForUserAgent } from "@/utils/userAgent";
 
 const URL =
   process.env.NEXT_PUBLIC_API_BASE_URL ||
@@ -60,11 +61,24 @@ class TimeoutInterceptor {
   }
 }
 
+// Sets a recognisable User-Agent on native API requests. Without this, requests
+// go out with the generic CFNetwork/Darwin (iOS) or okhttp (Android) UA.
+class UserAgentInterceptor {
+  async intercept(
+    request: Request<unknown, unknown>,
+    invoker: (request: unknown) => unknown,
+  ) {
+    request.getMetadata()["User-Agent"] = applicationNameForUserAgent;
+    return invoker(request);
+  }
+}
+
 const authInterceptor = new AuthInterceptor();
 const timeoutInterceptor = new TimeoutInterceptor();
+const userAgentInterceptor = new UserAgentInterceptor();
 
 const opts = {
-  unaryInterceptors: [authInterceptor, timeoutInterceptor],
+  unaryInterceptors: [userAgentInterceptor, authInterceptor, timeoutInterceptor],
   // this modifies the behaviour on the API so that it will send cookies on the requests
   withCredentials: true,
   /// TODO: streaming interceptor for auth https://grpc.io/blog/grpc-web-interceptor/