HOLI-9524: use index and fix distance calculation

* query now (implicitly) uses the HNSW index on embedding_array
* query now uses the `<#>` operator to sort by distance which can (and will) take advantage of the
  index for the newly introduced `location_gps` column which combines (`longitude`,`latitude`) into
  a PostGIS geometry
* distance calculation is fixed - it calculated before with two different units (distance in
  "angle" (RSID 4326) vs. distance in meters (RSID 3857, Pseudo-Mercator plane projection))