[DOP-15650] Allow using Horizon with multiple uvicorn workers

[dolfinus]

Change Summary

Few small adjustments to backend logging & usage examples to enable uvicorn workers.

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 91.50%. Comparing base (4313940) to head (7eb2e43).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop      #60   +/-   ##
========================================
  Coverage    91.50%   91.50%           
========================================
  Files          120      120           
  Lines         2449     2449           
  Branches       240      240           
========================================
  Hits          2241     2241           
  Misses         162      162           
  Partials        46       46           

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