Let oak-solr-osgi start also in containers different than Jetty

To start a JettySolrRunner Jetty dependencies are needed but that would fail on platforms different than Jetty as such dependencies are not embedded; however it doesn't make sense to start a JettySolrRunner under e.g. Tomcat so such dependencies will be marked as optional and therefore trying to instantiate a JettySolrRunner via EmbeddedSolrServerProvider with HTTP bindings will fail on such platforms.