Autoconvert legacy geoboxes

[SpacemanPaul]

Reason for this pull request

If you pass in a legacy GeoBox to dc.load() you eventually get an error from deep in the loading code

This is the 1.9 equivalent of @robbibt 's #1551 PR to 1.8.

Proposed changes

• Check for legacy datacube.utils.geometry.GeoBox objects in the datacube.Datacube API before calling loading code and convert to odc.geo.geobox.GeoBox.

• Unit test

• do class check without importing the deprecated legacy class to avoid deprecation warnings.

• Tests added / passed

• Fully documented, including docs/about/whats_new.rst for all changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.78%. Comparing base (a8ec892) to head (7424bcb).

Additional details and impacted files

@@               Coverage Diff               @@
##           develop-1.9    #1574      +/-   ##
===============================================
+ Coverage        85.58%   85.78%   +0.19%     
===============================================
  Files              140      140              
  Lines            15384    15386       +2     
===============================================
+ Hits             13167    13199      +32     
+ Misses            2217     2187      -30     

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[Ariana-B]

lgtm