Added a3 module for land cover as well as unit tests covering this module.

[tebadi]

The classes in this module were obtained from the following two sources to match the existing C2 product:

https://knowledge.dea.ga.gov.au/data/product/dea-land-cover-landsat/?tab=details
https://bitbucket.org/au-eoed/livingearth_lccs/src/1e78111ead2feb1179bf9fb30f6e8744aed65886/colour_schemes/lccs_l4_colour_scheme_golden_dark_au.csv

[codecov]

Codecov Report

Attention: Patch coverage is 96.72131% with 4 lines in your changes missing coverage. Please review.

Project coverage is 80.49%. Comparing base (a504ed5) to head (f5afd71).

Files with missing lines	Patch %	Lines
odc/stats/plugins/lc_veg_bare_water_a3.py	95.12%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #156      +/-   ##
===========================================
+ Coverage    80.04%   80.49%   +0.45%     
===========================================
  Files           49       51       +2     
  Lines         4359     4481     +122     
===========================================
+ Hits          3489     3607     +118     
- Misses         870      874       +4     

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