[ML] Fix Transforms not retaining _meta on clone (elastic#116206)

* [ML] Retain _meta on clone

* [ML] Fix validation on schema to only check it it's defined/not null

* [ML] Remove validation because es should handle the validation already

* Change type to unknown

x-pack/plugins/transform/common/api_schemas/transforms.ts

@@ -94,6 +94,13 @@ function transformConfigPayloadValidator<
   }
 }
 
+export const _metaSchema = schema.object(
+  {},
+  {
+    unknowns: 'allow',
+  }
+);
+
 // PUT transforms/{transformId}
 export const putTransformsRequestSchema = schema.object(
   {
@@ -112,6 +119,11 @@ export const putTransformsRequestSchema = schema.object(
     settings: schema.maybe(settingsSchema),
     source: sourceSchema,
     sync: schema.maybe(syncSchema),
+    /**
+     * This _meta field stores an arbitrary key-value map
+     * where keys are strings and values are arbitrary objects (possibly also maps).
+     */
+    _meta: schema.maybe(_metaSchema),
   },
   {
     validate: transformConfigPayloadValidator,

x-pack/plugins/transform/common/types/transform.ts

@@ -24,6 +24,7 @@ export type TransformBaseConfig = PutTransformsRequestSchema & {
   create_time?: number;
   version?: string;
   alerting_rules?: TransformHealthAlertRule[];
+  _meta?: Record<string, unknown>;
 };
 
 export interface PivotConfigDefinition {

x-pack/plugins/transform/public/app/common/request.ts

@@ -242,6 +242,7 @@ export const getCreateTransformRequestBody = (
         },
       }
     : {}),
+  ...(transformDetailsState._meta ? { _meta: transformDetailsState._meta } : {}),
   // conditionally add additional settings
   ...getCreateTransformSettingsRequestBody(transformDetailsState),
 });

x-pack/plugins/transform/public/app/sections/create_transform/components/step_details/common.ts

@@ -27,6 +27,7 @@ export interface StepDetailsExposedState {
   transformSettingsDocsPerSecond?: number;
   valid: boolean;
   indexPatternTimeField?: string | undefined;
+  _meta?: Record<string, unknown>;
 }
 
 const defaultContinuousModeDelay = '60s';
@@ -94,6 +95,10 @@ export function applyTransformConfigToDetailsState(
         state.transformSettingsDocsPerSecond = transformConfig.settings.docs_per_second;
       }
     }
+
+    if (transformConfig._meta) {
+      state._meta = transformConfig._meta;
+    }
   }
   return state;
 }

x-pack/plugins/transform/public/app/sections/create_transform/components/step_details/step_details_form.tsx

@@ -292,6 +292,7 @@ export const StepDetailsForm: FC<StepDetailsFormProps> = React.memo(
         touched: true,
         valid,
         indexPatternTimeField,
+        _meta: defaults._meta,
       });
       // custom comparison
       /* eslint-disable react-hooks/exhaustive-deps */