rev python api documentation

[jreiberkyle]

Revise python api documentation to match quality of CLI documentation.

Currently the python api documentation is disjointed from a reader perspective, as it was built up piece by piece as code was written. Revise the documentation to match the CLI story flow, using the same user stories and paths whenever possible.

Some specifics:

• on the topic of async, keep it simple and focused on the bit of code needed to get the task done (save 'async best practices' story arc for a later effort)
• when discussing creating, waiting, and downloading an order/asset, be sure to address how bulk ordering may differ from small batch ordering (ref: https://github.com/planetlabs/planet-client-python/issues/974#issuecomment-1640997565_)

[jreiberkyle]

planning meeting idea: separate ticket for revising python docs for async calls.