Update Github action workflows for v2

[timcnicholls]

This PR updates the Github action workflows in preparation for the v2 release. Changes include:

• adding a PyPI trusted publisher workflow to enable package publication
• Update the existing test CI workflow to latest releases of actions and pruning of obsolete Slack notifications
• Cleanup of coverage configuration files

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (acbcd40) to head (20af0b6).
⚠️ Report is 1 commits behind head on dev_2.0.

Additional details and impacted files

@@            Coverage Diff            @@
##           dev_2.0       #84   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         1674      1674           
=========================================
  Hits          1674      1674           

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[JamesOHeaDLS]

Looks good to me