Add filter ext

[matthewhanson]

Related Issue(s): #
#96

Description:
Add cql-json support

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #100 (371e020) into main (48ba65b) will decrease coverage by 0.31%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #100      +/-   ##
==========================================
- Coverage   79.02%   78.71%   -0.32%     
==========================================
  Files           9        9              
  Lines         534      545      +11     
==========================================
+ Hits          422      429       +7     
- Misses        112      116       +4     

Impacted Files	Coverage Δ
pystac_client/item_search.py	85.10% <62.50%> (-0.80%)	⬇️
pystac_client/cli.py	61.94% <66.66%> (+0.12%)	⬆️
pystac_client/version.py	100.00% <100.00%> (ø)

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