Fix ESCCRRestTestCase.verifyAutoFollowMonitoring (elastic#97054) (elastic#97104)

The method `verifyAutoFollowMonitoring` searches for
`ccr_auto_follow_stats` documents in `monitoring-es-*` indices to see if
one document has the field `number_of_successful_follow_indices` greater
than 0.

If such document is found, it means that x-pack monitoring successfully
indexed documents about CCR stats and that CCR at that time had at least
1 following index successfully running.

But the current `verifyAutoFollowMonitoring` method only check the first
10 docs returned by the search requests. Recent failures of
`AutoFollowIT.testAutoFollowPatterns` on 7.17 branch indicates that more
than 10 docs were found, so I suspect one of them has
`number_of_successful_follow_indices` > 0 but is not returned in the
first 10 top docs.

This pull request changes the method to only count documents with
`number_of_successful_follow_indices` > 0.

Closes elastic#91984

Author: tlrx

x-pack/plugin/ccr/qa/src/main/java/org/elasticsearch/xpack/ccr/ESCCRRestTestCase.java

@@ -217,9 +217,23 @@ protected static void verifyCcrMonitoring(final String expectedLeaderIndex, fina
     }
 
     protected static void verifyAutoFollowMonitoring() throws IOException {
-        Request request = new Request("GET", "/.monitoring-*/_search");
+        Request request = new Request("GET", "/.monitoring-*/_count");
         request.setJsonEntity("""
-            {"query": {"term": {"type": "ccr_auto_follow_stats"}}}""");
+                {
+                  "query": {
+                    "bool" : {
+                      "filter": {
+                        "term" : { "type" : "ccr_auto_follow_stats" }
+                      },
+                      "must" : {
+                        "range" : {
+                          "ccr_auto_follow_stats.number_of_successful_follow_indices" : { "gt" : 0 }
+                        }
+                      }
+                    }
+                  }
+                }
+            """);
         String responseEntity;
         Map<String, ?> response;
         try {
@@ -229,25 +243,12 @@ protected static void verifyAutoFollowMonitoring() throws IOException {
             throw new AssertionError("error while searching", e);
         }
         assertNotNull(responseEntity);
-        int numberOfSuccessfulFollowIndices = 0;
-
-        List<?> hits = (List<?>) XContentMapValues.extractValue("hits.hits", response);
-        assertThat(hits.size(), greaterThanOrEqualTo(1));
-
-        for (int i = 0; i < hits.size(); i++) {
-            Map<?, ?> hit = (Map<?, ?>) hits.get(i);
-
-            int foundNumberOfOperationsReceived = (int) XContentMapValues.extractValue(
-                "_source.ccr_auto_follow_stats.number_of_successful_follow_indices",
-                hit
-            );
-            numberOfSuccessfulFollowIndices = Math.max(numberOfSuccessfulFollowIndices, foundNumberOfOperationsReceived);
-        }
 
+        final Number count = (Number) XContentMapValues.extractValue("count", response);
         assertThat(
-            "Unexpected number of followed indices [" + responseEntity + ']',
-            numberOfSuccessfulFollowIndices,
-            greaterThanOrEqualTo(1)
+            "Expected at least 1 successfully followed index but found none, count returned [" + responseEntity + ']',
+            count.longValue(),
+            greaterThanOrEqualTo(1L)
         );
     }