Add Github CI and switch to Bitnami RabbitMQ container

[Lance-Drane]

What this does change

• Adds Github action for basic linting and testing
• Removes all references of our custom broker image in favor of a Bitnami one (so users no longer have to authenticate with code.ornl.gov). This includes both the local development environment AND the documentation.

What this does not do

• does not add codecoverage yet, may need to tweak the CI/CD command
• does not add the publishing CD yet (this should be in a separate file from CI)
• There are still references to utilizing the Docker container from the code.ornl.gov registry in the documentation, we should change this. (Users can at least build the image from source, we may or may not want to host prebuilt images ourselves.)

[marshallmcdonnell]

Awesome work! LGTM!

And kudos on getting the windows + macOS stuff already figured out as well!