Allow to disable addMockFSIndexStore test plugin (#93473)

The MockFSIndexStore randomizes the store type index 
settings in tests. It also throws random I/O exceptions 
and checks the index when shards are closed.

This behavior is sometimes unwanted in tests, but today 
tests cannot change the default random behavior. This 
change allows to disable this test plugin on specific tests.

Author: tlrx

test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java

@@ -2056,6 +2056,13 @@ protected boolean addMockInternalEngine() {
         return true;
     }
 
+    /**
+     * Returns {@code true} if this test cluster can use the {@link MockFSIndexStore} test plugin. Defaults to true.
+     */
+    protected boolean addMockFSIndexStore() {
+        return true;
+    }
+
     /**
      * Returns a function that allows to wrap / filter all clients that are exposed by the test cluster. This is useful
      * for debugging or request / response pre and post processing. It also allows to intercept all calls done by the test
@@ -2072,7 +2079,7 @@ protected Collection<Class<? extends Plugin>> getMockPlugins() {
             if (randomBoolean() && addMockTransportService()) {
                 mocks.add(MockTransportService.TestPlugin.class);
             }
-            if (randomBoolean()) {
+            if (addMockFSIndexStore() && randomBoolean()) {
                 mocks.add(MockFSIndexStore.TestPlugin.class);
             }
             if (randomBoolean()) {