feat: implement watch for monitoring chat messages

- Added a new command handler for /watch that allows users to listen to messages from a specified chat and save them according to storage rules.
- Introduced filtering options for messages using regular expressions.
- Implemented functionality to start and stop watching chats, including error handling for invalid inputs and user settings.
- Created a new utility package for message element handling related to the watch feature.
- Updated the user model to manage watched chats, including methods to add, remove, and check if a chat is being watched.

client/bot/handlers/utils/msgelem/save.go

@@ -10,6 +10,6 @@ const (
 
 	2. 设置默认存储后, 发送 /save <频道ID/用户名> <消息ID范围> 来批量保存文件. 遵从存储规则, 若未匹配到任何规则则使用默认存储.
 	示例:
-	/save @moreacg 114-514
+	/save @acherkrau 114-514
 	`
 )

client/bot/handlers/utils/msgelem/watch.go

@@ -0,0 +1,19 @@
+package msgelem
+
+const (
+	WatchHelpText = `
+	使用 /watch 命令监听一个聊天的消息, 并自动保存到默认存储中, 遵从存储规则.
+
+	命令语法:
+	/watch <chat_id> [filter]
+
+	参数:
+	- <chat_id>: 聊天的 ID 或用户名
+	- [filter]: 可选, 格式为 过滤器类型:表达式 , 所有支持类型的过滤器请查看文档
+
+	命令示例:
+	/watch 2229835658 msgre:.*plana.*
+
+	这将监听 ID 为 2229835658 的聊天, 并转存所有包含 "plana" 的媒体消息
+	`
+)