feat: Log of Nextcloud file synchronization in app

[QubaB]

Since I use Saber "professionally" and therefore depend on correct synchronization, it is useful to know when the synchronization is not working. Accessing the Saber log files is not trivial for the average user.

I implemented a display of the last 20 file synchronizations on the Nextcloud configuration page.

It could help with nextcloud troubleshooting, for example #382, #410

[codecov]

Codecov Report

Attention: Patch coverage is 27.77778% with 39 lines in your changes are missing coverage. Please review.

Project coverage is 37.33%. Comparing base (986f5e8) to head (ac41826).
Report is 6 commits behind head on main.

Files	Patch %	Lines
lib/components/nextcloud/log_messages.dart	26.31%	28 Missing ⚠️
lib/data/nextcloud/file_syncer.dart	30.00%	7 Missing ⚠️
lib/components/nextcloud/login_group.dart	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1151      +/-   ##
==========================================
- Coverage   37.37%   37.33%   -0.04%     
==========================================
  Files         108      109       +1     
  Lines        8497     8554      +57     
==========================================
+ Hits         3176     3194      +18     
- Misses       5321     5360      +39     

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