Replace travis-ci

[ni-jfitzger]

• This contribution adheres to CONTRIBUTING.md.
• [ ] I've updated CHANGELOG.md if applicable.
• [ ] I've added tests applicable for this pull request

What does this Pull Request accomplish?

Travis has stopped accepting our requests for builds.
GitHub Actions and workflows is something we're trying to standardize on for CI, anyway, and has the advantage of being free.

This restores our CI Checks by replacing Travis CI with a GitHub workflow.

It sets up a CI/PR workflow that will run on PRs and on merges to master.
All of the steps that were run by Travis-CI have been preserved but we now do things a bit more sensibly.

• We check that codegen is up to date before any other steps.
  • We do this with the version that we use for codegen, only.
• We run all of our various build checks (pkg, build_test, docs, flake8) with the version that we use for codegen, only.
• We run our API unit tests on all supported versions of Python and upload coverage results

Files specific to Travis have been eliminated.
Travis references have been deleted.
The Travis Badge in the READMEs has been replaced.

This change is largely based on nidaqmx-python workflows.

List issues fixed by this Pull Request below, if any.

• Fix Travis-CI has stopped accepting PR Triggers #2202

What testing has been done?

The new PR checks are running on this PR.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.51%. Comparing base (b6458aa) to head (eb6cf18).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2201      +/-   ##
==========================================
- Coverage   88.69%   88.51%   -0.18%     
==========================================
  Files          59       82      +23     
  Lines       18722    21679    +2957     
==========================================
+ Hits        16606    19190    +2584     
- Misses       2116     2489     +373     

Flag	Coverage Δ
codegenunittests	84.90% <ø> (?)
nidcpowersystemtests	94.38% <ø> (+0.04%)	⬆️
nidcpowerunittests	89.53% <ø> (?)
nidigitalsystemtests	92.02% <ø> (ø)
nidigitalunittests	68.44% <ø> (?)
nidmmsystemtests	92.29% <ø> (ø)
nifakeunittests	86.01% <ø> (?)
nifgensystemtests	94.32% <ø> (ø)
nimodinstsystemtests	73.85% <ø> (ø)
nimodinstunittests	94.20% <ø> (?)
nirfsasystemtests	82.66% <ø> (ø)
nirfsgsystemtests	81.12% <ø> (ø)
niscopesystemtests	89.96% <ø> (ø)
niscopeunittests	43.20% <ø> (?)
nisesystemtests	91.50% <ø> (ø)
niswitchsystemtests	81.56% <ø> (ø)
nitclksystemtests	94.87% <ø> (ø)
nitclkunittests	98.26% <ø> (?)

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see 27 files with indirect coverage changes

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[ni-jfitzger]

TODO: Maybe this action shouldn't be named unit_tests.yml. It's doing more than just running unit tests. Maybe CI.yml.

[ni-jfitzger]

TODO: Maybe this action shouldn't be named unit_tests.yml. It's doing more than just running unit tests. Maybe CI.yml.

I renamed and split it.