[AutoReply] Enable a hook to retrieve welcome message on new member join group

[hailiang-wang]

Description

When people join group, after resolving the peer bot, send the bot a message as on board hook.

Solution

For example,

{
    "fromUserId": "{{groupName}}",
    "textMessage": "__welcome_new_member_onboard",
    "faqBestReplyThreshold": 0.6,
    "faqSuggReplyThreshold": 0.35,
    "extras": {username: talker.name()}
}

About extras, check out
https://docs.chatopera.com/products/chatbot-platform/references/sdk/chatbot/chat.html#%E6%A3%80%E7%B4%A2%E5%A4%9A%E8%BD%AE%E5%AF%B9%E8%AF%9D