Improve handling of file name clashes

[claucambra]

This PR introduces two changes:

1. File name clashes are treated as warnings and not sync-stopping errors, much like invalid filenames
2. Clicking on an activity for a file name clash opens the relevant file in the web UI, where the file name clash can be resolved

Closes #4963

[codecov[bot]]

Codecov Report

Merging #4970 (664a80c) into master (38bc1e2) will not change coverage. The diff coverage is 0.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4970   +/-   ##
=======================================
  Coverage   57.12%   57.12%           
=======================================
  Files         138      138           
  Lines       17232    17232           
=======================================
  Hits         9844     9844           
  Misses       7388     7388           

Impacted Files	Coverage Δ
src/libsync/bulkpropagatorjob.cpp	73.10% <ø> (ø)
src/libsync/owncloudpropagator.cpp	85.88% <ø> (ø)
src/libsync/progressdispatcher.cpp	51.17% <ø> (ø)
src/libsync/propagatedownload.cpp	64.46% <0.00%> (-0.30%)	:arrow_down:
src/libsync/syncfileitem.h	37.50% <ø> (ø)
src/libsync/syncresult.cpp	9.57% <0.00%> (ø)
src/libsync/vfs/cfapi/cfapiwrapper.cpp	74.65% <0.00%> (+0.22%)	:arrow_up:
src/libsync/propagateremotemkdir.h	50.00% <0.00%> (+50.00%)	:arrow_up:

[nextcloud-desktop-bot]

AppImage file: nextcloud-PR-4970-664a80cbb5c9327dd956f2aa74703277cee7659f-x86_64.AppImage

To test this change/fix you can simply download above AppImage file and test it.

Please make sure to quit your existing Nextcloud app and backup your data.

[sonarqubecloud[bot]]

Please retry analysis of this Pull-Request directly on SonarCloud.

[claucambra]

/backport to stable-3.6