[Feature Request] Per-application Pub/Sub integration

Hi there!
It would be nice to have a per-application Pub/Sub integration. I know that LoraAppServer already has a global integration but in my case, triggering a app-specific function for every message received in every application is not very efficient.

Anyways I can use HTTP trigger and it works just fine, but Pub/Sub is a bit faster in GCP Cloud Functions cold starts.

Thanks in advance!