added support for SPARQL endpoint as repository
- extended the RdfRepositoryProducer to support SPARQL endpoints as repository backends.
- added username and password as optional properties used for secured HTTP and SPARQL endpoints that require authentiation
Tested with
- Ontotext GraphDB 10.3.0 (docker image: ontotext/graphdb:10.3.0)
- Franz Inc. AllegroGraph 7.3.1 (docker image: franzinc/agraph)
- Apache Jena Fuseki 4.9.0 (https://repo1.maven.org/maven2/org/apache/jena/jena-fuseki-docker/4.9.0/ )