Enable support for google storage buckets

[tom-butler]

Reason for this pull request

When pointing datacube at a google storage url (gs://) it threw Unexpected server error: Expecting URL with scheme here

Proposed changes

• register the gs:// scheme

• fix spacing issue in test_index_duplicate_dataset

• Tests added / passed

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

[Kirill888]

👍

[codecov]

Codecov Report

Merging #653 into develop will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #653      +/-   ##
===========================================
+ Coverage    87.78%   87.78%   +<.01%     
===========================================
  Files          101      101              
  Lines         8774     8775       +1     
===========================================
+ Hits          7702     7703       +1     
  Misses        1072     1072

Impacted Files	Coverage Δ
datacube/utils/uris.py	99.01% <100%> (ø)	⬆️

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[coveralls]

Coverage increased (+0.001%) to 87.738% when pulling e7b1847 on register-gs-scheme into ae1161d on develop.