Add XarraySourceConfig to allow specifying an XarraySource from STAC Items

[AdeelH]

Overview

This PR defines XarraySourceConfig, STACItemConfig, and STACItemCollectionConfig so that an XarraySource can be specified using STAC Items, e.g. those returned by a STAC API.

This allows STAC Items to be used directly with the Raster Vision pipeline. In particular: this can be combined with the new predict_scene (#1979) command to easily run predictions on imagery queried from a STAC API.

Checklist

• Added needs-backport label if PR is bug fix that applies to previous minor release
• Ran scripts/format_code and committed any changes
• Documentation updated if needed
• PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

• See new unit tests.

[codecov]

Codecov Report

Merging #1980 (1afb81d) into master (a7d56de) will increase coverage by 0.02%.
The diff coverage is 91.17%.

@@            Coverage Diff             @@
##           master    #1980      +/-   ##
==========================================
+ Coverage   86.18%   86.21%   +0.02%     
==========================================
  Files         193      195       +2     
  Lines        9499     9567      +68     
==========================================
+ Hits         8187     8248      +61     
- Misses       1312     1319       +7     

Files	Coverage Δ
...e/rastervision/core/data/raster_source/__init__.py	100.00% <100.00%> (ø)
...astervision/core/data/raster_source/stac_config.py	100.00% <100.00%> (ø)
...on/core/data/raster_source/xarray_source_config.py	84.21% <84.21%> (ø)

... and 1 file with indirect coverage changes