[Feature] Support for Watches

[RobsonSutton]

Watcher feature: To allow for management of watches via Terraform

Watcher API's: https://www.elastic.co/guide/en/elasticsearch/reference/current/watcher-api.html

Supported Elasticsearch Go Client functions:

• api.xpack.watcher.ack_watch.go
• api.xpack.watcher.activate_watch.go
• api.xpack.watcher.deactivate_watch.go
• api.xpack.watcher.delete_watch.go
• api.xpack.watcher.execute_watch.go
• api.xpack.watcher.get_watch.go
• api.xpack.watcher.put_watch.go
• api.xpack.watcher.query_watches.go
• api.xpack.watcher.start.go
• api.xpack.watcher.stats.go
• api.xpack.watcher.stop.go

Note: Resource should be able to accept an entire Watch config, via a single watch body attribute (to keep consistency with UI - instead of separating elements of a Watch config between separate attributes of the resource). Both approaches could potentially be made available though, if of value to end users!

[RobsonSutton]

Will be available in next version release (0.6.0) - Closing Issue