[FEATURE] Migrate Create/Update/Validate Detector using RestHighLevelClient

[dbwiddis]

Is your feature request related to a problem?

This is a summary issue replacing validate detector #217 and all its sub-issues #221, #222, #223, #224, #225, and #226 and replaces Create Detector functionality of #58, and adds Update Detector functionality (not yet tracked in an issue).

All three of these implementations share the same set of parent classes in the AD Plugin, so implementing one would create a large diff with duplicate classes. By waiting to submit a PR until all are complete the existing classes can all be replaced, the diff will be smaller and much more understandable/useful to future migration efforts.

What solution would you like?

• Migrate the RestIndexAnomalyDetectorAction which implements POST (Create) and PUT (Update) functionality
• Complete Create Detector workflow
  • Implement SearchFeatureDao component
  • Implement GetFieldMappingsAction (deferred) [FEATURE] Implement AD TransportGetFieldMappingsAction #361
• Complete Update Detector workflow
  • Complete getDetector() functionality
  • Implement ADTaskManager component (deferred) [FEATURE] Implement ADTaskManager component #371
• Migrate the RestValidateAnomalyDetectorAction which implements validate functionality
• Complete Validate Detector Workflow
  • Some "dryRun" boolean code paths may not have been tested and will require further updates
  • There may be additional steps required for validate detector model which may be moved to a new issue
• Replace existing classes with migrated versions of classes to minimize the diff
• Create a MIGRATING.md document to help future migrators
• Fix or bypass failing tests
  WIP is on this fork: https://github.com/dbwiddis/anomaly-detection/tree/rhlc

[dbwiddis]

Completed in AD #792