Dockerfile: remove test deps from prod image

[pjonsson]

Only install the test dependencies in
in the image used by the CI.

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📚 Documentation preview 📚: https://datacube-ows--1059.org.readthedocs.build/en/1059/

[pjonsson]

I started with a small change, but in the end this turned out to be larger than I had hoped for. Don't see any obvious way to split this though, so here we go.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.64%. Comparing base (2da24e5) to head (8a86cd3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1059   +/-   ##
=======================================
  Coverage   93.64%   93.64%           
=======================================
  Files          43       43           
  Lines        6510     6510           
=======================================
  Hits         6096     6096           
  Misses        414      414