[Backport 8.15] Added/updated snippets for docs (#2319)

(cherry picked from commit f737290d10)

Co-authored-by: Josh Mock <joshua.mock@elastic.co>

docs/doc_examples/f3574cfee3971d98417b8dc574a91be0.asciidoc

@@ -0,0 +1,44 @@
+// This file is autogenerated, DO NOT EDIT
+// Use `node scripts/generate-docs-examples.js` to generate the docs examples
+
+[source, js]
+----
+const response = await client.indices.create({
+  index: "idx",
+  mappings: {
+    _source: {
+      mode: "synthetic",
+    },
+    properties: {
+      flattened: {
+        type: "flattened",
+      },
+    },
+  },
+});
+console.log(response);
+
+const response1 = await client.index({
+  index: "idx",
+  id: 1,
+  document: {
+    flattened: {
+      field: [
+        {
+          id: 1,
+          name: "foo",
+        },
+        {
+          id: 2,
+          name: "bar",
+        },
+        {
+          id: 3,
+          name: "baz",
+        },
+      ],
+    },
+  },
+});
+console.log(response1);
+----