Create NodeEvents Chore on satellite core to read nodeevents DB and
notify node operators on node events. The chore sends notifications
grouped by email and event type: it selects the oldest entry in
nodeevents.DB and also any other event with the same email and event
type no matter how old it is. The oldest entry of a group must exist for
a minimum amount of time before that group can be selected, however.
This minimum amount of time is a configurable value:
--node-events.selection-wait-period. This wait period allows us to
combine events of the same time and same email address into a singular
email.
Change-Id: I8b444aa324d2dae265cc27d9e9e85faef79195d8
