Sorting multiple bitstreams/files in submission forms is not possible

[olli-gold]

Is your feature request related to a problem? Please describe.
For items with multiple attached bitstreams/files it may be necessary to show them in a specific order. In the database there is a field for that, bundle2bitstream.bitstream_order, but I do not see a chance how to change the order from the frontend.

Describe the solution you'd like
I would like to have a chance to modify the sort order of files in the submission form.

Describe alternatives or workarounds you've considered
As far as I know, there is no workaround besides the very dirty and not recommendable option to modify the database directly.

Additional context
I'm actually not sure, if this is a feature request for the frontend or the backend, but since I'm missing something in the frontend, I'm putting the issue on that side. However, it may be necessary to change or add something in the backend as well to implement that...