Allow configuring facet that are automatically expanded in Solr search

A client asked for auto expansion of a particular facet in Solr search. reading the code of xwiki-platform-core/xwiki-platform-search/xwiki-platform-search-solr/xwiki-platform-search-solr-ui/src/main/resources/Main/SolrSearchMacros.xml, I saw nothing that could allow this.

Workaround for the wiki facet:

window.addEventListener("DOMContentLoaded", function () {
  var facet = document.querySelector(".search-facet[data-name=wiki]");
  console.log("FACET", facet)
  if (facet) {
    facet.classList.add("expanded");
{{  }}}
})