Transition Azure Pipelines to Github Actions

[chapman39]

Migrates Azure Pipelines to GitHub Actions.

Some benefits:

• You can now cancel a job at any point.
• More storage (14GB instead of Azure's 10GB) (sources: azure, github actions).
• Jobs will no longer run on push. They will only run if there is an update to a pull request.
• Previous of a PR jobs are automatically canceled if an update has been made.
• Fails fast. If one job fails, the entire pipeline will cancel.
• You can re-try failed jobs.

Things todo that I can't do:

• Make GitHub Actions required to pass before merging into develop https://stackoverflow.com/a/60779334
• Remove Azure pipeline LLNL.serac

fixes #1265

[chapman39]

alternative to hacky solution for setting docker image name vars: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables#creating-configuration-variables-for-a-repository

but this would require users to access admin settings every time docker images are updated.

[chapman39]

I'm not sure how to remove the azure pipeline LLNL.serac from the ci checks.

[tupek2]

Chris should weigh in.