Add path_prefix parameter to cloud delivery option

[guyon-planet]

I would like a parameter in the delivery options that allows me to add a prefix.

I know the API allows it: https://developers.planet.com/docs/subscriptions/delivery/...

Describe the solution you'd like

Describe alternatives you've considered

Additional context

[pl-gideon]

@guyon-planet I plan to get around to this ... soon - it is low effort and valuable, thanks for creating an issue for it.