Add tests, configure GitLab CI, and add DDEV support for local development

Work on this has been performed in MR !23 (closed) over longer period of time. This MR was created in order to clean up the git history while preserving attribution to both developers who contributed to MR !23 (closed). It was created by starting with the up-to-date feature branch, cherry picking all the commits (except merges) from the MR !23 (closed) then squashing them into 2 commits - one commit for each of the contributors who worked on MR !23 (closed).

Closes #3349331