Add Docker login to GitLab CI
We had removed the Docker login command from the before_script in our CI pipeline, but that's problematic if the runner isn't already logged in.
During the maintenance period on Monday, 14 Oct 2024, all new projects will no longer create a container registry as part of the project area. Already existing projects will be unaffected at this time. Instead, users should utilize the official ORNL container registries at camden.ornl.gov (internal/moderate) and savannah.ornl.gov (external/low). Please see ORNL Today article for more info.
We had removed the Docker login command from the before_script in our CI pipeline, but that's problematic if the runner isn't already logged in.