Support multiple levels of filepaths in generic packages repository

Currently, we can upload files into the generic package registry, however we cannot organize our generic packages well.

There's the first level, which you can use to name the group as a whole. Then there's of course the version field, to indicate the software version. But finally, there is no way to group the actual files.

e.g. if My filepath looks like:

"${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/${_group_name}/${CI_COMMIT_TAG#v}/${_file_name}"

it would be nice to also do

"${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/${_group_name}/${CI_COMMIT_TAG#v}/${_sublevel}/${_file_name}"

The UI should be able to handle this quite well, with a > expandable.