More dynamic local-storage-provisioner approach (#3472)

* Makes local volume provisioner more dynamic

* Correct variable name in local storage provisioner defaults

* Updates external-provisioner readme

* Updates variable naming to be more clear, more documentation, fixes sample inventory

* Variable refactor, untangled some jinja2 loops

* Corrects variable name

* No variable substitution in dict keys, replaced with anchor

* Fixes default storage_classes dict, inline docs

* Fixes spelling in inline docs

* Addresses comments in review

* Updates all the defaults

* Fix failing CI task

* Fixes external provisioner daemonset