[feature]: add a new `SubscribeAllSendEvents` RPC call that enables backlog delivery + on going subscription

[Roasbeef]

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

Today we have a SubscribeSendEvents RPC call. It gives notifications for on going send events, but only those that are actively underway in the porter. So in the event of an offline client, or restart, a client needs to do a series of other queries to be able to receive consistent notifications.

Describe the solution you'd like

We should make a new call, SubscribeAllSendEvents that provides reliable notifications for all past and on going sends. It should accept either a ID, or timestamp, deliver the backlog based on that, then listen for new incoming notifications.