Switch CI tests to GH Actions with publishing workflow

[dhomeier]

Description

Replace Azure with GH Actions via reusable workflows from https://github.com/OpenAstronomy/github-actions-workflows, including a standard publishing workflow.

[codecov]

Codecov Report

Merging #17 (160636a) into main (08bda43) will increase coverage by 0.24%.
The diff coverage is n/a.

❗ Current head 160636a differs from pull request most recent head 18b1150. Consider uploading reports for the commit 18b1150 to get more accurate results

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   85.78%   86.03%   +0.24%     
==========================================
  Files           8        8              
  Lines         401      401              
==========================================
+ Hits          344      345       +1     
+ Misses         57       56       -1     

Impacted Files	Coverage Δ
glue_plotly/html_exporters/scatter2d.py	82.52% <0.00%> (+0.97%)	⬆️

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[dhomeier]

Should publish get a test_command to run on the built wheel?

[astrofrog]

Yes I think ideally we should do it as for glue-core, if at all possible

[dhomeier]

Seems to work with the same setup. I have just opened glue-viz/glue#2308 to add the needs: tests there (with allowed_failures factored out, which is not needed here :) and also added the codecov.yml as used in astropy, to try and set just a minimal nonzero threshold. Apparently codecov is not required to pass, so that's not strictly necessary.
And also copying from the astropy setup here the initial run of codestyle before anything else is started; what do you think about that?

[astrofrog]

Running codestyle before the rest seems sensible to me - this looks good, thanks!