Parse CI variables

Users will often create model candidates from CI, and we can link the candidate to the job/mr/author using the CI variables. Initially, we will be asking users to log these by adding the following snippet to their tracking code:

if os.getenv('GITLAB_CI'):
    mlflow.set_tags({'gitlab.CI_JOB_ID': os.getenv('CI_JOB_ID')})

While these might be already stored, we need to parse them and create the UI to display them.