Allow query by OSMID instead of Nominatim name

Useful sometimes to find specific places that are annoying. In my example some Italian cities gave their urban areas first instead of the municipality boundaries.

Request from Clement Sebastiao @csebastiao

Start by locating the Nominatim name-query entry point and tracing how place results are selected. Define how an OSMID should be accepted and verify that it can return the intended municipality boundaries rather than a different urban area.

Written by the indexing model from the issue text.