Log transaction durations (#2682)

There can be delays in releasing predicate locks when we have
transactions that are long-lived -- even delays in releasing predicate
locks acquired by shorter-lived transactions. Logging the transaction
duration will allow us to get a sense as to transaction durations during
busy times.

core/src/main/java/google/registry/persistence/transaction/JpaTransactionManagerImpl.java

@@ -276,6 +276,10 @@ public class JpaTransactionManagerImpl implements JpaTransactionManager {
       }
       T result = work.call();
       txn.commit();
+      long duration = clock.nowUtc().getMillis() - txnInfo.transactionTime.getMillis();
+      if (duration >= 100) {
+        logger.atInfo().log("Transaction duration: %d milliseconds", duration);
+      }
       return result;
     } catch (Throwable e) {
       // Catch a Throwable here so even Errors would lead to a rollback.