[DAR-4305][External] Cancel push operations if there are no valid files to upload, and correctly remove invalid files

[JBWilkie]

Problem

There are 2 minor issues that were released with multi-file push in 1.0.10:

• When pruning files to upload based on the full filepaths currently in the dataset - If we remove any multi-file items, we don't correctly remove the corresponding LocalFile objects. This leads to duplicate warnings
• If after pruning files to upload, there are no files left - The importer should stop and display this to the user. Currently it continues then displays:

All 0 files have been successfully uploaded.

Solution

• Only display a warning for each LocalFile to be removed if it hasn't already been added to the list of local files to be removed as a result of being tied to a MultiFileItem
• Raise a ValueError if there are no MultiFileItem or LocalFile objects left to upload after pruning

Changelog

Improved error messaging when attempting to upload duplicate files

[linear]

DAR-4305 Cancel `push` operations if there are no valid files to upload, and correctly remove invalid files