support json output directly from Nominatim dump, without database

[gcar-bendingspoons]

When dumping to JSON, support loading the data from a Nominatim dump instead of the database.

The goal of this change is to preprocess the JSON data dumps available from Graphhopper before importing in Komoot search service.

• Update README with new -json <output filename> -input-file <nominatim dump filename>
• Separate PR for adding the address type to the output

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch dump-from-file

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[lonvia]

I don't understand what you want to do here. If you need to preprocess the JSON dumps you can do that with any other tool that can process json before importing them to Photon.