Generic message types for internal management

[vertexclique]

We need some internal management for message types.

Lifecycle Commands (exposed)

• [x] Stop (stops polling exec or stops the children group's elements or supervised elements)
• [x] Kill (stops polling exec or cancels the children group's elements or supervised elements)
• [x] Start (start polling exec or start the children group's elements or supervised elements)

Notifications

• [x] Dead (when exec successfully finished its executiong or Stop/Kill was received or one the elements of the children group stopped)
• [x] Faulted (when exec panics or returns an error or one elements of the children group faulted)

Direct Communication (exposed)

• [x] Tell (a message)
• [x] Ask (a message with a channel to answer with another message)

Remote Communication (exposed)

• [x] Deploy (makes a supervisor supervise a new children group or supervisor)
• [ ] Prune (TODO)
• [x] SuperviseWith (changes the supervision strategy of a supervisor)

[r3v2d0g]

@vertexclique is Prune still needed?

(Note that it is present in bastion but not used ~~or supported~~ though supported by System.)

[vertexclique]

We can close this but having another issue for Remote Communication would be nice.

[r3v2d0g]

@vertexclique Maybe Prune could be used to stop/kill a Children/Supervisor and completely remove it (ie. not restarting it even if it was supervised by a "one-for-all" supervisor)?

[vertexclique]

That is the main idea of it. especially on distributed communication. So I think this can go under bastion-rs/artillery. Though we still need to iterate on this.