[Feature Request]: Allow learners to subscribe to a classroom to receive updates

[AFZL210]

Is your feature request related to a problem? Please describe.

As we are adding more classrooms and topics to existing classrooms, it would be good for learners to subscribe to a classroom to receive emails whenever a new topic is added. This way, they can stay updated with the latest topics and continue learning new concepts.

Describe the solution (or solutions) you'd like

On the classroom page, add a "Subscribe" button. When users hover over it, display a tooltip with the text "Receive emails whenever a new topic is added to this classroom." Upon clicking this button, they should be added to a mailing list or similar specifically for that classroom.

And also allow learners to unsubscribe from the classroom.

Describe alternatives you've considered and rejected

No response

Additional context

No response