add flake8 and pylint to lint workflow

[pindge]

Reason for this pull request

When commits are checked by pre-commit and flake8 code lint was corrected, it applies to lines that were committed without flake8 causing extra lines of changes shown in a pull request increasing difficulty in reviewing.

Adding flake8 to code lint as part of GitHub action ensures commits with or without pre-commit checks are all passing flake8 code lint.

Proposed changes

• create lint.yaml for code lint run as part of PR action

• add flake8 for code lint as per pre-commit hook

• streamline github action, move pycodestyle and pylint out of build and into lint

• apply flake8 lint correction to all effected lines

• add more ignore to setup.cfg

• Closes Flake is used in pre-commit but not in github action #1284

• Tests added / passed

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

[codecov]

Codecov Report

Merging #1285 (d5db048) into develop (7045532) will decrease coverage by 0.04%.
The diff coverage is 79.45%.

@@             Coverage Diff             @@
##           develop    #1285      +/-   ##
===========================================
- Coverage    93.47%   93.43%   -0.05%     
===========================================
  Files          128      128              
  Lines        12958    12953       -5     
===========================================
- Hits         12113    12103      -10     
- Misses         845      850       +5     

Impacted Files	Coverage Δ
datacube/api/grid_workflow.py	97.08% <ø> (-0.05%)	⬇️
datacube/drivers/postgis/_schema.py	100.00% <ø> (ø)
datacube/drivers/postgis/sql.py	98.18% <ø> (ø)
datacube/drivers/postgres/_schema.py	100.00% <ø> (ø)
datacube/drivers/postgres/sql.py	98.18% <ø> (ø)
datacube/helpers.py	26.31% <ø> (-7.02%)	⬇️
datacube/index/memory/_fields.py	90.90% <ø> (ø)
datacube/index/memory/_users.py	100.00% <ø> (ø)
datacube/index/null/_users.py	100.00% <ø> (+10.00%)	⬆️
datacube/index/postgis/_metadata_types.py	96.20% <ø> (-0.05%)	⬇️
... and 42 more

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[SpacemanPaul]

Some minor comments on a very large but minor PR.

Happy to debate any of them if anybody disagrees with my takes.