Backport developer environment changes

Backport changes from https://gitlab.developers.cam.ac.uk/uis/devops/iam/identity/identity-system/-/merge_requests/8 and https://gitlab.developers.cam.ac.uk/uis/devops/iam/identity/identity-system/-/merge_requests/9 into this repository.

Those changes remove the ui module. It is still useful to have a ui module and so, instead, either make the ui module optional or split the boilerplate into a pure API one and a full-featured webapp one.