Support for basic authentication (collection control)

[pigeon-geng]

@kiranchitturi
I see the #118 . Why not like this

val options = Map(
  "collection" -> "{solr_collection_name}",
  "zkhost" -> "{zk_connect_string}",
  "httpBasicAuthUser" -> "{httpBasicAuthUser}",
  "httpBasicAuthPassword" -> "{httpBasicAuthPassword}",
)
val df = spark.read.format("solr")
  .options(options)
  .load

This seems to be more friendly to multi-permission support.
It can be controlled by spark options.

[kiranchitturi]

We didn't add this due to the auth being exposed but if the opts are controlled via external variable, then this does make sense. Patches are welcome

[washcycle]

I was looking for this feature as well. I use the solr-operator in k8s and have a lot of solr instances and right now I have to have a Spark cluster designated for each instance of solr. I'd like to be able to switch on the fly. The patch implemented looked good to me.