[frontend] center loader (#8280)

[frapuks]

Proposed changes

• center loader

Related issues

• close Loader in knowledge graph should be position at center vertically, not at the top #8280

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

[Archidoit]

Behavior and code ok but maybe need to rebase for the Drone tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.14%. Comparing base (c986eae) to head (bffaaea).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8386   +/-   ##
=======================================
  Coverage   66.13%   66.14%           
=======================================
  Files         597      597           
  Lines       60382    60382           
  Branches     6190     6192    +2     
=======================================
+ Hits        39935    39937    +2     
+ Misses      20447    20445    -2     

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