* Adds kafka, URI, and JDBC namespace defintions
* Add ability to explicitly rename using a "namespace" which is a particular data collection that is loaded on all realtime, historic nodes, and brokers. If any of these nodes has the namespace extension, ALL nodes have the namespace extension.
* Add namespace caching and populating (can be on heap or off heap)
* Add NamespaceExtractionCacheManager for handling caches
* Added ExtractionNamespace for handling metadata on the extraction namespaces
* Added ExtractionNamespaceUpdate for handling metadata related to updates
* Add extension which caches renames from a kafka stream (requires kafka8)
* Added README.md for the namespace kafka extension
* Added docs
* Added namespace/size, namespace/count, namespace/deltaTasksStarted metrics
Add static config for namespaces via `druid.query.extraction.namespace`
* This is a rebase of https://github.com/b-slim/druid/tree/static_config_only
Charles Allen
Himanshu Gupta