Add CI integration

Add CI integration to knowledge gap repo (.gitlab-ci.yml).

• Run unit tests
• Run integration test; run content pipeline in local mode, check it completes successfully and generates output data
• The "deployment" of the content gap pipeline is tracked in #3; which involves adding jobs to ci; e.g. triggering building a conda envs for main (and possibly development branches)

Generally, the goal is to establish a good template configuration that follows good practices and can serve as a starting point for other repositories that will be added by researchers.