add canonical ref to item links

[Ariana-B]

See #228

Add another item link that points to the location of the stac json file on S3 as the 'canonical' reference.

Pin shapely version < 2.0.0.

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📚 Documentation preview 📚: https://datacube-explorer--510.org.readthedocs.build/en/510/

[codecov]

Codecov Report

Base: 86.46% // Head: 86.47% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (d23aced) compared to base (a4b435a).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #510      +/-   ##
===========================================
+ Coverage    86.46%   86.47%   +0.01%     
===========================================
  Files           26       26              
  Lines         3427     3430       +3     
===========================================
+ Hits          2963     2966       +3     
  Misses         464      464              

Impacted Files	Coverage Δ
cubedash/_stac.py	86.37% <100.00%> (+0.10%)	⬆️

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