File transfer of remaining files should continue in background when file name conflicts occur

### Problem

When backing up many files to a network drive (~1.5 Million files with ~3TB in total), the file transfer got stuck after about 7 GB because some of the files were already present from a previous backup attempt
I left the PC after starting the copy and then came back after some hours and was expecting the transfer would already have been done.
Instead of the file transfer being almost done, no real progress was made as the dialog that asks whether to overwrite the conflicting file was still open waiting for an answer

### Proposal

Continue the non-conflicting file transfers in the background automatically, do the transfers with conflicts last once the option (replace vs. skip) was chosen

### Prior Art (Optional)

_No response_