Add missing Javadoc for MonitoredResourceMapping

Author: psx95

exporters/metrics/src/main/java/com/google/cloud/opentelemetry/metric/MonitoredResourceMapping.java

@@ -19,20 +19,40 @@
 import java.util.Set;
 import javax.annotation.concurrent.Immutable;
 
+/**
+ * This class holds the mapping between Google Cloud's monitored resource type and the labels for
+ * identifying the given monitored resource type.
+ */
 @Immutable
 public final class MonitoredResourceMapping {
  private final String mrType;
  private final Set<String> mrLabels;
 
+ /**
+ * Public constructor.
+ *
+ * @param mrType The monitored resource type for which the mapping is being specified.
+ * @param mrLabels A set of labels which uniquely identify a given monitored resource.
+ */
  public MonitoredResourceMapping(String mrType, Set<String> mrLabels) {
  this.mrType = mrType;
  this.mrLabels = mrLabels;
  }
 
+ /**
+ * Returns the set of labels used to identify the monitored resource represented in this mapping.
+ *
+ * @return Immutable set of labels that map to the specified monitored resource type.
+ */
  public Set<String> getMonitoredResourceLabels() {
  return Collections.unmodifiableSet(mrLabels);
  }
 
+ /**
+ * The type of the monitored resource for which mapping is defined.
+ *
+ * @return The type of the monitored resource.
+ */
  public String getMonitoredResourceType() {
  return this.mrType;
  }