Add support for Private Network Access via Access-Control-Allow-Private-Network header

[artemdanylenko]

Relevant issues

Resolves #793

Contributor checklist

• [x] Provide tests for the changes (unless documentation-only)
• [x] Documented any new features, CLI switches, etc. (if applicable)
  • [x] Server --help output
  • [x] README.md
  • [x] doc/http-server.1 (use the same format as other entries)
• [x] The pull request is being made against the master branch

Maintainer checklist

• [ ] Assign a version triage tag
• [ ] Approve tests if applicable

[artemdanylenko]

cc @thornjad

[github-actions[bot]]

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