Persist messages between user sessions

[gabheadz]

Is your feature request related to a problem? Please describe.
There are scenarios, where processes takes several hours to complete and a notification would be desirable upon completion, even if the user is not longer connected.

Describe the solution you'd like

• When requesting to deliver a message to a user, and there's is no longer an active channel, persist message for a configurable period of time.
• Push such messages when the client initiates a new session and opens a channel.
• There is already a functionality to persist messages when clients looses connection temporarilly with channel-sender. But the proposed solution is aimed to persist messages between user sessions.

Describe alternatives you've considered

• None at the moment.

Additional context

• N/A