[DOP-23077] Improve documentation

[dolfinus]

Change Summary

• Add docstring to CredentialsEncryptionSettings, and add it to server, scheduler and worker settings documentation
• Add RequestIDSettings class to server settings documentation, use Horizon and DataRentgen as an example
• Fix references names in documentation
• Rearrange settings entries in .env values

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 0.00%. Comparing base (33918bc) to head (836b1af).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@      Coverage Diff       @@
##   develop   #175   +/-   ##
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