feat: add automated release management

Following instructions from the guidebook, enable release automation for this module.

Marked as draft pending https://gitlab.developers.cam.ac.uk/uis/devops/infra/gitlab-project-factory/-/issues/37.

The reviewer probably wants to do a bit of testing/additional checking since I believe this will be the first time we enable automated releases for a terraform module.

Closes #10 (closed)