Elastic: Fix error "e.buckets[Symbol.iterator] is not a function" when using filter (#26217)

* Add bucket to array if it is not in array

* Fix issue one level above

* Rename variable

* Move array check to processAggregationDocs

public/app/plugins/datasource/elasticsearch/elastic_response.ts

@@ -135,8 +135,8 @@ export class ElasticResponse {
       table.addColumn({ text: metricName });
       values.push(value);
     };
-
-    for (const bucket of esAgg.buckets) {
+    const buckets = _.isArray(esAgg.buckets) ? esAgg.buckets : [esAgg.buckets];
+    for (const bucket of buckets) {
       const values = [];
 
       for (const propValues of _.values(props)) {