[ML] Account for "properties" layer in find_file_structure mappings (#77035) (#77142)

This is the UI side companion for elastic/elasticsearch#62158

Previously the "mappings" field of the response from the
find_file_structure endpoint was not a drop-in for the
mappings format of the create index endpoint - the
"properties" layer was missing. The reason for omitting
it initially was that the assumption was that the
find_file_structure endpoint would only ever return very
simple mappings without any nested objects. However,
this will not be true in the future, as we will improve
mappings detection for complex JSON objects. As a first
step it makes sense to move the returned mappings closer
to the standard format.

Author: David Roberts

x-pack/plugins/ml/common/types/file_datavisualizer.ts

@@ -84,7 +84,12 @@ export interface Settings {
 }
 
 export interface Mappings {
-  [key: string]: any;
+  _meta?: {
+    created_by: string;
+  };
+  properties: {
+    [key: string]: any;
+  };
 }
 
 export interface IngestPipelineWrapper {

x-pack/plugins/ml/server/models/file_data_visualizer/import_data.ts

@@ -94,7 +94,7 @@ export function importDataProvider({ asCurrentUser }: IScopedClusterClient) {
         _meta: {
           created_by: INDEX_META_DATA_CREATED_BY,
         },
-        properties: mappings,
+        properties: mappings.properties,
       },
     };