Alert Notifications: Add Telegram Support

[Sonixier]

The Alert Notifications system supports only Discord right now.
This issue serves as a suggestion to add Telegram Support.

[jshufro]

Please vote here: https://dao.rocketpool.net/t/notification-channels-poll/2901

Note that it might be some time before we are able to roll out support for additional channels. We're blocked on a major refactor.