Allow use of feature references in the sdk

[angaither]

Related Issue(s):

Closes #

Proposed Changes:

For inclusion in changelog (if applicable):

1. Allow feature references to be used in the sdk for creating subscriptions (with or without a source block) and for orders.
2. Create a top level geometry filter in the data api, allow references and features there

Not intended for changelog:

Diff of User Interface

Old behavior:
geojson was required to make a subscription or order.

New behavior:
geojson or a geometry feature reference can be used

{
        "type": "ref",
        "content": "pl:features/my/water-fields-RqB0NZ5/rmQEGqm",
} 

Or in the cli a ref can be used as a string

 planet data search PSScene --geom 'pl:features/my/water-fields-RqB0NZ5/rmQEGqm' | jq

PR Checklist:

• This PR is as small and focused as possible
• If this PR includes proposed changes for inclusion in the changelog, the title of this PR summarizes those changes and is ready for inclusion in the Changelog.
• I have updated docstrings for function changes and docs in the 'docs' folder for user interface / behavior changes
• This PR does not break any examples or I have updated them

(Optional) @mentions for Notifications:

[ischneider]

There's a number of geometry: Optional[dict] though the typing intention is now including str (ref)

I haven't dug enough to see if it's even possible (or useful) to try to specify a GeoJSON type (like by applying more type variables to dict keys, though honestly it doesn't feel useful)...

But something like this might be a nice compromise (untested in mypy or other static checker)

from typing import Union

# GeoJSON is a python dict that conforms to the specification
GeoJSON = dict

# GeoRef is a reference to a feature, either as a file or URI, that if resolved, would yield GeoJSON
GeomRef = str

# Geom is some inline or reference to a Geometry
Geom = Union[GeoJSON, GeomRef]

[asonnenschein]

I see this MR includes integration tests for the Data API/CLI, and the Subscriptions CLI. @angaither Do you think we also need tests for the Subscriptions API and Orders API/CLI?

[angaither]

I see this MR includes integration tests for the Data API/CLI, and the Subscriptions CLI. @angaither Do you think we also need tests for the Subscriptions API and Orders API/CLI?

We probably only need CLI tests since that is doing a bit more manipulation and allowing strings, so I added a test for the orders CLI.
The API tests probably aren't needed since

1. we are just passing values through to the respective APIs and this feature is already tested in those codebases
2. They're mocked clients