This diff adds a singleton class for a publisher in the Tunnelbroker client integration into the Tunnelbroker. The publisher class uses connect() method to make a connection to the Tunnelbroker for the publisher. This approach is inspired by our Redis approach with the changes that we are connecting to the Tunnelbroker ahead of time (on server start) instead of on publishing like in the Redis implementation. I think it's a good way to make a connection ahead of time, but this can be changed if reviewers think otherwise.
Linear task: ENG-2613