SPARQL query documentation and redirection link for the old public SPARQL endpoint

[jonquet]

This issue is about updating the documentation related to SPARQL query and the backend triple store in the OntoPortal documentation:
https://ontoportal.github.io/documentation/administration/management/reference_sparql_endpoint

With the change of triple-store on the BioPortal (AllegroGraph) and AgroPortal/BiodivPortal (Virtuoso) side.

Plus, on AgroPortal side, we need to redirect to the URLs:
https://sparql.agroportal.lirmm.fr/
and
https://sparql.agroportal.lirmm.fr/test/

That were made public to the documentation page explaining how to connect to our SPARQL endpoint and fire SPARQL queries agains AGroPOrtal (see also #684)