Alias support for virtual products

[uchchwhash]

Reason for this pull request

• Add alias support for virtual products
• Fix geopolygon bug

[codecov]

Codecov Report

Merging #612 into develop will increase coverage by 0.02%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #612      +/-   ##
===========================================
+ Coverage    86.41%   86.44%   +0.02%     
===========================================
  Files           84       84              
  Lines         8100     8101       +1     
===========================================
+ Hits          7000     7003       +3     
+ Misses        1100     1098       -2

Impacted Files	Coverage Δ
datacube/virtual/utils.py	78.37% <ø> (-1.11%)	⬇️
datacube/virtual/impl.py	89.75% <100%> (+0.12%)	⬆️
datacube/model/__init__.py	86.95% <0%> (+0.62%)	⬆️

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[ashoka1234]

Looks good.

[ashoka1234]

Looks good

[coveralls]

Coverage increased (+0.03%) to 86.421% when pulling 143e6cb on virtual-product-aliases into 27dce16 on develop.