Add Solr Basic Auth Support

**Describe the feature:**
I don't see any way to provide basic auth information for Solr Like there is for ElasticSearch. It would be great if this was possible.

**Describe a specific use case for the feature:**
I'm currently using the the solr operator to run a solr cluster in cloud mode with the basic auth plugin https://apache.github.io/solr-operator/docs/solr-cloud/solr-cloud-crd.html. When I use janusgraph with this authentication fails.

No files or tests are named in the issue. Start by locating the existing Elasticsearch authentication configuration and the Solr integration, then compare how credentials are passed to each backend. Done means JanusGraph can authenticate to a Solr cloud using basic-auth credentials, with coverage for the reported Solr operator use case.

Written by the indexing model from the issue text.