feat: itchat support joingroup message

plugins/hello/hello.py

@@ -23,7 +23,16 @@ class Hello(Plugin):
         logger.info("[Hello] inited")
 
     def on_handle_context(self, e_context: EventContext):
-        if e_context["context"].type != ContextType.TEXT:
+        if e_context["context"].type not in [ContextType.TEXT, ContextType.JOIN_GROUP]:
+            return
+
+        if e_context["context"].type == ContextType.JOIN_GROUP:
+            e_context["context"].type = ContextType.TEXT
+            msg: ChatMessage = e_context["context"]["msg"]
+            e_context[
+                "context"
+            ].content = f'请你随机使用一种风格说一句问候语来欢迎新用户"{msg.actual_user_nickname}"加入群聊。'
+            e_context.action = EventAction.CONTINUE  # 事件继续，交付给下个插件或默认逻辑
             return
 
         content = e_context["context"].content