Add support for Apache Ranger authorizer

[Jimvin]

Users wishing to use an existing Apache Ranger for authorization in NiFi should be able to configure this. It requires that the Ranger NAR file is loaded into the NiFi lib directory and that the configuration outlined in the following link is applied to the NiFi instance - https://cwiki.apache.org/confluence/display/RANGER/NiFi+Plugin

• Document how to include custom processors in a Stackable NiFi deployment #229
• Operator support ranger-provider in authorizers.xml
• Operator support for ranger-nifi-audit.xml and ranger-nifi-security.xml configuration
• Test LDAP authentication with Ranger authorization

[Jimvin]

This feature request can likely be closed if we can offer;

1. an alternative means of authorisation, either internal NiFi authorisation or using OPA
2. the ability to log audit events from NiFi (see Audit events for NiFi #515)