Add property to disable model caching

This is mostly for the integration tests of the Gradle Enterprise Maven extension,
which heavily test dependency resolution and reuse the same GAVs in many test,
e.g. a:b:1.0. It would be a lot of effort to rewrite all those tests and a shame
to restart the daemon every time. So I wanted to ask if you'd consider this flag
to disable the caching altogether.

daemon/src/main/java/org/apache/maven/project/SnapshotModelCacheFactory.java

@@ -45,6 +45,9 @@ public SnapshotModelCacheFactory(DefaultModelCacheFactory factory) {
 
     @Override
     public ModelCache createCache(RepositorySystemSession session) {
-        return new SnapshotModelCache(globalCache, factory.createCache(session));
+        boolean enableModelCache = Boolean.parseBoolean(System.getProperty("mvnd.modelCache", "true"));
+        ModelCache reactorCache = factory.createCache(session);
+        ModelCache globalCache = enableModelCache ? this.globalCache : reactorCache;
+        return new SnapshotModelCache(globalCache, reactorCache);
     }
 }