Integration test config instructions

[SpacemanPaul]

Reason for this pull request

There were still some references to the postgis driver as "experimental" in docs and tests, especially integration tests.

Proposed changes

• Remove all references to the postgis driver as "experimental".

• Suppress ODC2 Deprecation warnings in unit tests.

• Tests added / passed

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

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📚 Documentation preview 📚: https://datacube-core--1693.org.readthedocs.build/en/1693/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.62%. Comparing base (63b65ff) to head (efa119c).
Report is 4 commits behind head on develop-1.9.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop-1.9    #1693   +/-   ##
============================================
  Coverage        85.61%   85.62%           
============================================
  Files              151      151           
  Lines            15526    15531    +5     
============================================
+ Hits             13293    13298    +5     
  Misses            2233     2233           

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