LPS-42802 Asset Publisher doesn't order content by recent date properly

\cc @dsanz 

Hi Ray,

Could you check if our changes make sense?

We need to index the dates as a numbers, because the method we are using to get the sort in AssetPublisher, if the field is a number, uses the sortable field instead of the field.

Another question, Do you know why we make a date format and we store it as keyword? and Why we don't store only the date in milliseconds?

Thanks!!

Eudaldo.