Allow users to toggle personal notifications

[christolis]

Describe the feature

To begin with, there should be a "🔕 Disable notifications" button on notification messages sent by the bot, which does exactly what the title of the button says. Notification messages include:

• Notifying the user that their streak is about to reset if they don't practice before the end of the day.
• Any other future reminders sent by the bot to the users.
• For a user to enable notifications again, they would have to use a command like: /notifications toggle. By default, every new user should be receiving them.
• Since we need to let users know about the existence of the above command, the "Disable notifications" button should notify users about the command as a side note.