Solr index the document content update date instead of the document date

When performing a search we discovered that the modification date presented for Video macro extensions and the actual modification date shown in the extension page were not matching.
Apparently, the date shown in the extension page was right, while the one presented in the search UI was wrong, presenting a date 4 years before the actual last modification.

This can wrong impressions for users thinking that the extensions are not maintained properly.