Query Elevation based on Filter Query "fq" field

(PR-2098)

This ticket introduces a new QueryElevation related feature. 

Currently, QueryElevationComponent is implemented and can be used to configure/customize the top results for a given query, depending on the field query "q" .

This ticket suggests an extension of this feature that allows users to configure the top results,  based on the Filter Query field "fq" as well.

Below is an example query.

Based on the "fq" field value, we would get, as top results, regardless of the normal Lucene scoring, the elements configured in elevate.xml schema.

  <query text="cat:electronics"> 
    <doc id="TWINX2048-3200PRO" /> 
    <doc id="VDBDB1A16" />   
    <doc id="EN7800GTX/2DHTV/256M" />
  </query>

Instead of having a classic value for the "text" field in the <query> tag in the code snippet above, introducing a Filter Query expression allows to configure top results for queries having the an "fq" field value containing "cat:electronics", and therefore, they will be returned in the top of the results list.