Allow the API to schedule an action to be executed, allowing to perform a series of actions on droplet.
The main objective is to allow to a droplet snapshot itself, scheduling an action to start within a couple of minutes or when the droplet is down.
It would be achieved in three ways:
1. This could be applied exclusively to snapshots, as a "snapshot_delay" action, which would start in 5 minutes, giving the user time to shutdown the system;
2. Actions could receive a "time_delay" parameter, which delays the execution of the action by "time_delay" seconds;
3. Actions could be triggered by events with an "on_event" parameter, allowing "snapshot" to be executed "on_event" "power_off"