Add new Docker tags for release channels

[nguyer]

This PR adds several new Docker tags which are used conditionally based on the git tag used when a GitHub release is created. The rules are as follows:

• If the release is a pre-release,
  • and the tag contains the string alpha then alpha tag will be applied to the Docker image
  • or if the tag contains the string beta then the beta tag will be applied to the Docker image
  • or if the tag contains the string rc then the rc tag will be applied to the Docker image
• Or if the release is not a pre-release,
  • The latest tag will be applied to the Docker image
• The head tag will always be applied to the image