Add Nats messenger (#3525)

bukkit/build.gradle

@@ -44,6 +44,7 @@ shadowJar {
     relocate 'com.mongodb', 'me.lucko.luckperms.lib.mongodb'
     relocate 'org.bson', 'me.lucko.luckperms.lib.bson'
     relocate 'redis.clients.jedis', 'me.lucko.luckperms.lib.jedis'
+    relocate 'io.nats.client', 'me.lucko.luckperms.lib.nats'
     relocate 'com.rabbitmq', 'me.lucko.luckperms.lib.rabbitmq'
     relocate 'org.apache.commons.pool2', 'me.lucko.luckperms.lib.commonspool2'
     relocate 'ninja.leaping.configurate', 'me.lucko.luckperms.lib.configurate'

bukkit/src/main/resources/config.yml

@@ -241,6 +241,8 @@ watch-files: true
 #                below.
 #   => rabbitmq  Uses RabbitMQ pub-sub to push changes. Your server connection info must be
 #                configured below.
+#   => nats      Uses Nats pub-sub to push changes. Your server connection info must be
+#                configured below.
 #   => custom    Uses a messaging service provided using the LuckPerms API.
 #   => auto      Attempts to automatically setup a messaging service using redis or sql.
 messaging-service: auto
@@ -266,6 +268,14 @@ redis:
   username: ''
   password: ''
 
+# Settings for Nats.
+# Port 4222 is used by default; set address to "host:port" if differs
+nats:
+  enabled: false
+  address: localhost
+  username: ''
+  password: ''
+
 # Settings for RabbitMQ.
 # Port 5672 is used by default; set address to "host:port" if differs
 rabbitmq: