title: Solr search facets name with regular expression
body: <p>I wanted to filter facets name based on regular expression. 
  I have an idea of facet.prefix element and im expecting an similar feature to find facets by providing keywords that can be somewhere in between the whole work.</p>
  
  <p>example :- facets country["united states","west indies","india"].
  required feature: search all facets name containing "ind" keyword. resulting "west indies" and "india".</p>