LockRegistryLeaderInitiator: Add DEBUG for errors

For better traceability for errors during lock acquiring add DEBUG
logging message in the `catch` block before returning back to the main
loop for the next acquiring attempt

**Cherry-pick to 5.0.x and 4.3.x**

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/support/leader/LockRegistryLeaderInitiator.java

@@ -400,6 +400,9 @@ else if (acquired) {
 							}
 							return null;
 						}
+						else if (logger.isDebugEnabled()) {
+							logger.debug("Error acquiring the lock. " + (isRunning() ? "Retrying..." : ""), e);
+						}
 					}
 				}
 			}