fix(event_handler): read swagger files with UTF-8 encoding

[JustinBerger]

Issue number: closes #8129

Summary

Changes

• When reading the swagger_ui js and css files, they are opened with UTF-8 encoding.

User experience

• The js and css files will be loaded as UTF-8 regardless of the default encoding set on the runtime environment. Other than fixing the bug, I would not expect this to have an impact on user experience.

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[boring-cyborg]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.64%. Comparing base (12aeb50) to head (82eff76).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8131   +/-   ##
========================================
  Coverage    96.64%   96.64%           
========================================
  Files          284      284           
  Lines        14079    14079           
  Branches      1153     1153           
========================================
  Hits         13606    13606           
  Misses         344      344           
  Partials       129      129           

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[leandrodamascena]

Hey @JustinBerger thanks a lot for sending this PR and contributing to Powertools!

APPROVED!

[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!