[DOP-23743] All hardcoded passwords in this repo are used ONLY for tests

[dolfinus]

Change Summary

This is to shut up security scanners or information security guys which think we are storing here some production passwords. No, they are used just for tests, and nothing more.

Also fixed several small issues with tests, like Clickhouse client haven't used database/user/password at all, password wasn't quoted in SQLAlchemy URLs used by Pandas, and so on.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.00%. Comparing base (78bf9f6) to head (78185cb).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #335      +/-   ##
===========================================
+ Coverage    91.69%   92.00%   +0.30%     
===========================================
  Files          228      228              
  Lines         9842     9842              
  Branches      1009     1009              
===========================================
+ Hits          9025     9055      +30     
+ Misses         621      598      -23     
+ Partials       196      189       -7     

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