[apache#1495] fix(core): Change the HashMap to ConcurrentMap in Proto…

…EntitySerDe (apache#1525)

### What changes were proposed in this pull request?
Fix ConcurrentModificationException threw in function
`ProtoEntitySerDe:getProtoClass()`

### Why are the changes needed?

Fix: apache#1495

### Does this PR introduce _any_ user-facing change?

NO

### How was this patch tested?

The TrinoQueryIT tester has been run successfully many times. However,
before this change, it sometimes fails due to a
ConcurrentModificationException

core/src/main/java/com/datastrato/gravitino/proto/ProtoEntitySerDe.java

@@ -60,8 +60,8 @@ public class ProtoEntitySerDe implements EntitySerDe {
   private final Map<Class<? extends Entity>, Class<? extends Message>> entityToProto;
 
   public ProtoEntitySerDe() {
-    this.entityToSerDe = Maps.newHashMap();
-    this.entityToProto = Maps.newHashMap();
+    this.entityToSerDe = Maps.newConcurrentMap();
+    this.entityToProto = Maps.newConcurrentMap();
   }
 
   @Override