Feat: base postgresql registry settings on registry database settings

What does this MR do?

Feat: base postgresql registry settings on registry database settings

• Change registry library priority from 20 to 19 to load before PostgreSQL, but still load after LetsEncrypt.
• Add parse_registry_postgresql_settings method to PostgreSQL library.
• Set PostgreSQL registry defaults based on registry configuration.
  • First user provided values, then registry defaults.
• Remove hardcoded PostgreSQL registry attributes, now set dynamically.

This addresses the technical debt discussed in issue #9216 (closed) by ensuring registry database configuration is the authoritative source, while PostgreSQL libraries use only postgresql[...] settings that are automatically populated from registry configuration when not explicitly set.

Changelog: changed

Related issues

Closes #9216 (closed)

Checklist

See Definition of done.

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Required

• MR title and description are up to date, accurate, and descriptive.
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• Latest Merge Result pipeline is green.
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For GitLab team members

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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
  • Added specs should be enough here, but I've also done 1 manual integration test for a possibly uncovered spec: !8623 (comment 2662827954).
• Documentation created/updated.
• Tests added.
• Integration tests added to GitLab QA.
• Equivalent MR/issue for the GitLab Chart opened.
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.