Migrate from CircleCI to GitHub Actions

[nhinsch]

What does this PR do?

Add a GitHub Actions workflow in the repo and remove the CircleCI configuration file. I will remove the CircleCI webhook after this is merged so that we no longer attempt to run CircleCI jobs.

Motivation

We are migrating from CircleCI to GitHub Actions.

Testing Guidelines

Manual testing to see that the new Workflows run.

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)