Disable MockTelemetryPlugin by default for integ tests (#12877)

With this plugin enabled we see significant increase in memory usage.
This is due to a static map that collects Span entries per write/replication request.
Tests with higher counts of independent writes are at risk of running oom or experiencing
slow down / warnings related to this.

Disabled the plugin by default until this is resolved given it is still under FeatureFlag.

Signed-off-by: Marc Handalian <marc.handalian@gmail.com>

Author: mch2

test/framework/src/main/java/org/opensearch/test/OpenSearchIntegTestCase.java

@@ -2070,7 +2070,8 @@ protected boolean addMockGeoShapeFieldMapper() {
      * @return boolean.
      */
     protected boolean addMockTelemetryPlugin() {
-        return true;
+        // setting to false until https://github.com/opensearch-project/OpenSearch/issues/12615 is resolved
+        return false;
     }
 
     /**