Create the mapping explicitly, otherwise for 0 documents indices (ela…

…stic#118015)

the mapping will not contain the "value" field

(cherry picked from commit 774c6ea)

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/RequestIndexFilteringTestCase.java

@@ -101,7 +101,7 @@ public void testFieldExistsFilter_KeepWildcard() throws IOException {
         indexTimestampData(docsTest1, "test1", "2024-11-26", "id1");
         indexTimestampData(docsTest2, "test2", "2023-11-26", "id2");
 
-        // filter includes only test1. Columns are rows of test2 are filtered out
+        // filter includes only test1. Columns and rows of test2 are filtered out
         RestEsqlTestCase.RequestObjectBuilder builder = existsFilter("id1").query("FROM test*");
         Map<String, Object> result = runEsql(builder);
         assertMap(
@@ -253,6 +253,9 @@ protected void indexTimestampData(int docs, String indexName, String date, Strin
                   "@timestamp": {
                     "type": "date"
                   },
+                  "value": {
+                    "type": "long"
+                  },
                   "%differentiator_field_name%": {
                     "type": "integer"
                   }