Allow to use custom subscription project in the full subscription name

[Shanjohn]

Is your feature request related to a problem? Please describe.
A third party firm provided our service user with access to a PubSub subscription. The subscription is located in their project, but active project should be our own - the one where we created the service user. Right now the full subscription name is automatically generated from cps.subscription and cps.project, but since the project to which we login and the project where subscription is located.

Describe the solution you'd like
I'd like to be able to specify the project to which the subscription belong as an additional parameter (e.g. cps.subscriptionProject), which defaults to the cps.project if not set.

Describe alternatives you've considered
Alternative solution might be to add an argument which allows specifying full subscription name instead of using CPS_SUBSCRIPTION_FORMAT

Additional context
Any other context or screenshots about the feature request.