Further automate build and release process

[sethmlarson]

We also have partially automated the release process in GitHub Actions but haven't reached the level of automation that we have for Windows and Azure Pipelines.

Currently run_release requires humans to click around in the GitHub UI to manually execute the GitHub workflow, which wasn't the case before. We also lost the automatic local testing step in favor of testing on GitHub Actions, but local assurance is good to have for RMs.

• Further automate kicking off the build and release workflows on GitHub Actions.
• Automatically detect workflow completion and download artifacts from GitHub Actions.
• Add back local testing to run_release.py script once artifacts are automatically downloaded.

cc @ambv