Add MQTT v5 properties support (meetecho#2273)

conf/janus.eventhandler.mqttevh.jcfg.sample

@@ -16,6 +16,7 @@ general: {
 							# plain (no indentation) or compact (no indentation and no spaces)
 
 	url = "tcp://localhost:1883"	# The URL of the MQTT server. Only tcp supported at this time.
+	#mqtt_version = "3.1.1"			# Protocol version. Available values: 3.1, 3.1.1 (default), 5.
 	client_id = "janus.example.com"	# Janus client id. You have to configure a unique ID (default: guest).
 	#keep_alive_interval = 20		# Keep connection for N seconds (default: 30)
 	#cleansession = 0				# Clean session flag (default: off)
@@ -46,4 +47,7 @@ general: {
 	#tls_client_key = "/path/to/key.pem"
 	#tls_ciphers
 	#tls_version
+
+	# These options work with MQTT 5 only.
+	#add_user_properties = ()	# List of user property ["key", "value"] pairs to add.
 }

conf/janus.transport.mqtt.jcfg.sample

@@ -28,6 +28,10 @@ general: {
 	#certfile = /path/to/cert.pem
 	#keyfile = /path/to/key.pem
 
+	# These options work with MQTT 5 only.
+	#vacuum_interval = 60					# Interval for removing old transaction states in seconds.
+	#proxy_transaction_user_properties = []	# Array of user property names to copy from the incoming message.
+	#add_transaction_user_properties = ()	# List of user property ["key", "value"] pairs to add.
 }
 
 admin: {