Add the option to replace Bitstreams when submitting a new version of an Item

[ybnd]

Is your feature request related to a problem? Please describe.

When submitting a new version of an Item it's common for its Bitstreams to change.
Currently, this requires the user to upload the new version and manually copy any custom metadata or access conditions from the original.

Describe the solution you'd like

We want to introduce a new option to the submission upload step to allow submitters to replace an existing Bitstream.

Additional information

REST issue: DSpace/DSpace#10504