feat: sent same notifications once only

[ErikKalkoken]

Some notifications are sent to all members of an alliance. If a use has more then one character in the same alliance he will get duplicates of the same notification for each character. This change ensures that only one instance of those duplicate notification is created as desktop/mobile notification.

Resolves #293

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.8%. Comparing base (f3651d9) to head (30560e1).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/app/storage/characternotification.go	33.3%	1 Missing and 1 partial ⚠️
internal/app/characterservice/communications.go	0.0%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #296   +/-   ##
=====================================
  Coverage   38.8%   38.8%           
=====================================
  Files        223     223           
  Lines      38572   38572           
=====================================
+ Hits       14991   15002   +11     
+ Misses     21681   21672    -9     
+ Partials    1900    1898    -2     

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