Add new listing strategy by tracking listed entities to ListXXXX processors

Current List processors (ListFile, ListFTP, ListSFTP ... etc) implementation relies on file last modified timestamp to pick new or updated files. This approach is efficient and lightweight in terms of state management, because it only tracks latest modified timestamp and last executed timestamp. However, timestamps do not work as expected in some file systems, causing List processors missing files periodically. See NIFI-3332 comments for details.

In order to pick every entity that has not seen before or has been updated since it had seen last time, we need another set of processors using different approach, that is by tracking listed entities:

• Add new abstract processor AbstractWatchEntries similar to AbstractListProcessor but uses different approach
• Target entities have: name (path), size and last-modified-timestamp
• Implementation Processors have following properties:
  • 'Watch Time Window' to limit the maximum time period to hold the already listed entries. E.g. if set as '30min', the processor keeps entities listed in the last 30 mins.
  • 'Minimum File Age' to defer listing entities potentially being written
• Any entity added but not listed ever having last-modified-timestamp older than configured 'Watch Time Window' will not be listed. If user needs to pick these items, they have to make 'Watch Time Window' longer. It also increases the size of data the processor has to persist in the K/V store. Efficiency vs reliability trade-off.
• The already-listed entities are persisted into one of supported K/V store through DistributedMapCacheClient service. User can chose what KVS to use from HBase, Redis, Couchbase and File (DistributedMapCacheServer with persistence file).
• The reason to use KVS instead of ManagedState is, to avoid hammering Zookeeper too much with frequently updating Zk node with large amount of data. The number of already-listed entries can be huge depending on use-cases. Also, we can compress entities with DistributedMapCacheClient as it supports putting byte array, while ManagedState only supports Map<String, String>.
• On each onTrigger:
  • Processor performs listing. Listed entries meeting any of the following condition will be written to the 'success' output FlowFile:
    • Not exists in the already-listed entities
    • Having newer last-modified-timestamp
    • Having different size
  • Already listed entries those are old enough compared to 'Watch Time Window' are discarded from the already-listed entries.
• Initial supporting target is Local file system, FTP and SFTP