[8.19][ES|QL] Fixes commands visibility (#224999)

## Summary

- Moves change_point to tech preview
- Hides fork


### Checklist
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

Author: stratoula

src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/__tests__/autocomplete.command.fork.test.ts

@@ -54,6 +54,7 @@ describe('autocomplete.suggest', () => {
           'WHERE ',
           'SORT ',
           'LIMIT ',
+          'CHANGE_POINT ',
           'DISSECT ',
           'STATS ',
           'EVAL ',

src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/commands.ts

@@ -594,7 +594,7 @@ export const commandDefinitions: Array<CommandDefinition<any>> = [
     suggest: suggestForJoin,
   },
   {
-    hidden: true,
+    hidden: false,
     name: 'change_point',
     preview: true,
     description: i18n.translate(
@@ -681,7 +681,7 @@ export const commandDefinitions: Array<CommandDefinition<any>> = [
     fieldsSuggestionsAfter: fieldsSuggestionsAfterChangePoint,
   },
   {
-    hidden: false,
+    hidden: true,
     name: 'fork',
     preview: true,
     description: i18n.translate('kbn-esql-validation-autocomplete.esql.definitions.forkDoc', {