[HUDI-3764] Allow loading external configs while querying Hudi tables with Spark (#4915)

Currently when doing Hudi queries w/ Spark, it won't 
load the external configurations. Say if customers enabled 
metadata listing in their global config file, then this would 
let them actually query w/o metadata feature enabled. 
This PR fixes this issue and allows loading global 
configs during the Hudi reading phase.

Co-authored-by: Wenning Ding <wenningd@amazon.com>

hudi-common/src/main/java/org/apache/hudi/common/config/DFSPropertiesConfiguration.java

@@ -196,6 +196,12 @@ public class DFSPropertiesConfiguration {
     return globalProps;
   }
 
+  // test only
+  public static TypedProperties addToGlobalProps(String key, String value) {
+    GLOBAL_PROPS.put(key, value);
+    return GLOBAL_PROPS;
+  }
+
   public TypedProperties getProps() {
     return new TypedProperties(hoodieConfig.getProps());
   }