More meaningful messages on Bulk Import errors if `bulk_import_enabled` is false
Starting with GitLab 15.8, the bulk_import_enabled
application setting needs to be enabled on the instance for bulk imports to work via the API.
When attempting to use the migrations/bulk imports API on default instance settings, this just gives a plain 404 as of 15.8 now (see !106590 (merged)).
This is very cryptic, at least compared to the feedback you get in the UI. We hit this as maintainers of an API client (https://github.com/python-gitlab/python-gitlab/pull/2494), I imagine it will be even more confusing for users who don't interact with the API as often. Would it make sense to at least hint that this is disabled on the instance in the error message?
/cc @JohnVillalovos
/cc also @georgekoltsov from the related MR :)