Add ability to set lens session params via config

We need to set a bunch of hive session params (job conf). It works when sets it via the lens cli through the "set x=y" api, which calls the "/lensapi/session/params" api on the server, which in turn calls HiveSessionService - setSessionParameter method. Only config-driven way to set these for the hive driver is by setting them in hivedriver-site.xml. This seems to be a lens limitation. Only "lens.session.aux.jars" can be set. Similarly we should be able to set "lens.session.params" with a list of comma-seperated key-value pairs as well. Also this, along with lens.session.aux.jars should be settable via a lens-cli config (not just server-side)