Added/updated snippets for docs (#2318)

docs/doc_examples/21565b72da426776e445b1a166f6e104.asciidoc

@@ -0,0 +1,20 @@
+// 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: "my-index-000001",
+  mappings: {
+    properties: {
+      "my-join-field": {
+        type: "join",
+        relations: {
+          parent: "child",
+        },
+      },
+    },
+  },
+});
+console.log(response);
+----