[validation-errors] Fixes in watcher API (elastic#1889)

* Adding cancelled properties as optional since is hides behind a `include_cancelled` param.

* Add UDF as a possible value for FieldValue

* changing input into a singlekey dictionnary to capture nesting

* Fixing compare & array_compare conditions

* Add codegen name for udf

* Fix inversion during refactoring

* Add refreshed schema & types

* Prettifying code

* Rename udf in favor of any

* Remove unused imports

* Update schema

Author: Anaethelion