[frontend] use new loader in report overview (#8288)

[frapuks]

Proposed changes

• use new loader in report overview
• use new loader in all widget
• remove WidgetLoader

Related issues

• close The 'entities overview' loader is not the one used in the rest of the application #8288

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case (coverage and e2e)
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.05%. Comparing base (66fa73c) to head (ad18b3a).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8385      +/-   ##
==========================================
- Coverage   66.06%   66.05%   -0.01%     
==========================================
  Files         597      597              
  Lines       60913    60913              
  Branches     6206     6203       -3     
==========================================
- Hits        40241    40238       -3     
- Misses      20672    20675       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.