Support for PostGIS in model geocoding

[kalsan]

Hi Alex!

I've read the discussion over in #1524 and while I fully agree that more complex geocalculations should be left to a dedicated gem, it would still be interesting to see PostGis support in geocoded_by.

Here's my current workaround:

class Foo < ApplicationRecord
  # has columns :address (string), :latitude (decimal), :longitude (decimal) and :coordinates (st_point)

  geocoded_by :address
  after_validation :geocode_postgis
  
  private

  def geocode_postgis
    geocode # fills latitude and longitude
    self.coordinates = "POINT(#{longitude} #{latitude})" # fills postgis
  end
end

While this is not too hard to accomplish, it would be even better to be able to have PostGIS support in geocoder, similar to support (geocoded_by: :coordinates)