[ML] Auto-generate kibana route schemas based on es client types

[jgowdyelastic]

For ML's endpoints which are basic wrappers for elasticsearch endpoints, it would be better if the validation schemas were generated based on the JSON structure definitions supplied by the es client. https://github.com/elastic/elastic-client-generator/blob/master/output/schema/schema.json

The json structure definition: https://github.com/elastic/elastic-client-generator/blob/master/compiler/model/metamodel.ts The typescript types generator: https://github.com/elastic/elastic-client-generator/blob/master/typescript-generator/index.ts

Relates to https://github.com/elastic/elastic-client-generator/issues/443

[elasticmachine]

Pinging @elastic/ml-ui (:ml)