Add option to telegram bot to subscribe to dappnode telegram announcements channel

[pablomendezroyo]

There could be considered two types of notifications:

1. Dappmanager notifications
2. Dappnode team notifications

The current implementation of the telegram bot allows the dappmanager to send notifications from the system to the user (if the telegram bot was configured).

In addition to this feature would be a nice to have an option to subscribe to the dappnode team notifications, mostly done through the discord announcements channel