Simplify subscription clip rules in the Subscriptions API SDK

[asonnenschein]

Problem:
In the HTTP Subscriptions API service contract, there is one place to specify the clip tool that covers custom clip and default clip (by omitting aoi and falling back to subscription source geometry).

In the Python SDK, users can specify a custom clip AOI via planet.subscription_request.clip_tool() OR they can fall back on the default clip (subscription source geometry) by defining planet.subscription_request.build_request() kwarg clip_to_source = True. So the default clip behavior is in a separate code path from the custom clip behavior. To add more confusion, if a user defines both clip_tool() and clip_to_source = True then the client will error.

Solution (updated with @wilsaj's feedback):
Keep the clip_to_source kwarg on the build_request() method, and remove the clip_tool() method. Subscriptions API no longer supports custom clip AOIs. Only two clip options are currently supported: clip to subscription source geometry, or don't clip to subscription source geometry. In build_request(), the clip_to_source=True logic can be simplified to appending "tools": [{"type": "clip", "parameters": {}}] to the request rather than copying the subscription source geometry into the tool parameters, and Subscriptions API will automatically clip to the subscription source geometry. The clip_to_source=False logic should be default, and not append any clip tool options to the request.

[wilsaj]

I don't see any reason to support custom clip AOIs in the SDK, since the Subscription API does not support them. Clipping is really just a binary option in the API: either clip to the Subscription geometry or don't clip at all.

Custom clip AOIs used to be supported, but that was removed a while ago. The clip tool still accepts an AOI parameter for backwards compatibility, but requires that the clip AOI must match the subscription geometry and will return a validation error if it doesn't match.

[asonnenschein]

#1169