Support encrypted channels

Echo is mainly designed around Pusher real-time model for client and server.
Pusher natively supports encrypted channels as per https://pusher.com/docs/channels/using_channels/encrypted-channels/.
Ably also supports encryption for payload https://ably.com/docs/realtime/encryption.
The secret key should be distributed to private and presence channels, right next to the ably-capability key, look at first feature - modify channel capability.
Though, encryption works a bit differently in ably, it can be implemented at a certain point.
This feature is not yet explicitly requested by users but can be prioritized once the requirement comes.

ably-forks / laravel-echo