GH-3348: Upgrade to MQTT Paho-1.2.4

Fixed https://github.com/spring-projects/spring-integration/issues/3348

**Cherry-pick to 5.3.x, 5.2.x & 5.1.x**

# Conflicts:
#	build.gradle

build.gradle

@@ -84,7 +84,7 @@ ext {
 	mockitoVersion = '3.3.3'
 	mongoDriverVersion = '4.0.4'
 	mysqlVersion = '8.0.20'
-	pahoMqttClientVersion = '1.2.2'
+	pahoMqttClientVersion = '1.2.4'
 	postgresVersion = '42.2.12'
 	reactorVersion = 'Dysprosium-SR8'
 	resilience4jVersion = '1.4.0'