Edit PullSubscription config if config was passed in method.

[chandr-andr]

Hello! Thank you for this awesome library.
I've found implicit behavior with the method pull_subscribe.

Problem:

After you shut down your worker with a pull-based subscription, the consumer continues to exist in Nats, and when you start your worker with the method pull_subscribe config doesn't change.
For example, a push-based subscription acts vice versa.

Solution:

So, I think it's better to edit the configuration every time you want to create a pull-based subscription. Because if you change your subscription configuration you expect that it will be changed in the nats.

If I missed something important, please, explain)