Break apart GHA workflow

[mattwelke]

Right now, the GHA workflow does the build and push to Docker Hub, and it's running on pull request. Instead, we need two workflows:

• test - runs tests upon pull requests to main
• build_and_deploy - builds the Docker image and deploys it to Docker Hub upon pushes to main

That way we won't have pull requests causing Docker Images to be built and we'll have something in place to run tests.