[NEW] Add support to the event ":userId:/message" subscription

[rafaelks]

Description

The app needs to add support for this event subscription over stream-notify-user subscription:

:userId:/message

The call is basically:

let request = [
    "msg": "sub",
    "name": "stream-notify-user",
    "params": ["\(user.identifier ?? "")/message", false]
]

The thing is, when getting messages over this event, we'll have to set to the message these two properties:

• private: true
• user: {"username": "rocket.cat", "_id": "rocket.cat"}

This is because the messages coming from this stream needs to be removed on every new session.

The messages that are coming from this subscription: private messages only related to that user; Examples:

1. Commands replies;
2. Rocket.Chat Apps replies;