fix docs, add test

Author: smalyshev

docs/changelog/129013.yaml

@@ -7,6 +7,7 @@ highlight:
   title: Add remote index support to LOOKUP JOIN
   body: |-
     Queries containing LOOKUP JOIN now can be preformed on cross-cluster indices, for example:
-    ```
+    [source,yaml]
+    ----------------------------
     FROM logs-*, remote:logs-* | LOOKUP JOIN clients on ip | SORT timestamp | LIMIT 100
-    ```
+    ----------------------------

x-pack/plugin/esql/qa/server/multi-clusters/src/javaRestTest/java/org/elasticsearch/xpack/esql/ccq/MultiClustersIT.java

@@ -505,7 +505,14 @@ public void testLookupJoinAliasesSkipOld() throws IOException {
             mapMatcher = mapMatcher.entry("_clusters", any(Map.class));
             mapMatcher = mapMatcher.entry("is_partial", true);
             assertMap(result, mapMatcher.entry("columns", columns).entry("values", values));
-            // TODO: check that the remote is skipped
+            // check that the remote is skipped
+            @SuppressWarnings("unchecked")
+            Map<String, Object> clusters = (Map<String, Object>) result.get("_clusters");
+            @SuppressWarnings("unchecked")
+            Map<String, Object> details = (Map<String, Object>) clusters.get("details");
+            @SuppressWarnings("unchecked")
+            Map<String, Object> remoteCluster = (Map<String, Object>) details.get("remote_cluster");
+            assertThat(remoteCluster.get("status"), equalTo("skipped"));
         } finally {
             wipeLookupIndices();
         }