[ES|QL] Support the CHANGE_POINT command

[stratoula]

Describe the feature:

This PR elastic/elasticsearch#120998 added support on the CHANGE_POINT command. (it is on snapshot releases)

We will need to:

• Support in client side validation
• Support in prettifier
• Support in ast parser
• Support in autocomplete

This command is used for change point detection (ML command). The syntax goes like:

FROM k8s
  | STATS count=COUNT() BY @timestamp=BUCKET(@timestamp, 1 MINUTE)
  | CHANGE_POINT count ON @timestamp AS type, pvalue

More examples here https://github.com/elastic/elasticsearch/blob/main/x-pack/plugin/esql/qa/testFixtures/src/main/resources/change_point.csv-spec

[elasticmachine]

Pinging @elastic/kibana-esql (Team:ESQL)