Expose started time in ActivityInfo (temporalio#1798)

Author: Quinn-With-Two-Ns

temporal-sdk/src/main/java/io/temporal/activity/ActivityInfo.java

@@ -66,6 +66,13 @@ public interface ActivityInfo {
    */
   long getScheduledTimestamp();
 
+  /**
+   * Time when the Activity Task (current attempt) was started.
+   *
+   * @return Timestamp in milliseconds (UNIX Epoch time)
+   */
+  long getStartedTimestamp();
+
   /**
    * Time when the Activity Task (current attempt) was scheduled by the Temporal Server.
    *

temporal-sdk/src/main/java/io/temporal/internal/activity/ActivityInfoImpl.java

@@ -82,6 +82,11 @@ public long getScheduledTimestamp() {
     return Timestamps.toMillis(response.getScheduledTime());
   }
 
+  @Override
+  public long getStartedTimestamp() {
+    return Timestamps.toMillis(response.getStartedTime());
+  }
+
   @Override
   public long getCurrentAttemptScheduledTimestamp() {
     return Timestamps.toMillis(response.getCurrentAttemptScheduledTime());
@@ -183,6 +188,8 @@ public String toString() {
         + getActivityType()
         + ", scheduledTimestamp="
         + getScheduledTimestamp()
+        + ", startedTimestamp="
+        + getStartedTimestamp()
         + ", currentAttemptScheduledTimestamp="
         + getCurrentAttemptScheduledTimestamp()
         + ", scheduleToCloseTimeout="