Record the actor on assign, archive and unarchive (#35)

Assign logged only the assignee (user_id), archive/unarchive logged nothing.
Migration 018 adds actor_user_id/actor_service_account_id to incident_events
for 'assigned'; archive/unarchive now log archived/unarchived events with the
caller via callerActorIDs. Timeline JSON gains actor_* fields; web timeline
renders them. Service accounts are still not assignable.

internal/api/incident_store.go

@@ -32,6 +32,8 @@ const (
 	evAcknowledged   = "acknowledged"
 	evUnacknowledged = "unacknowledged"
 	evAssigned       = "assigned"
+	evArchived       = "archived"
+	evUnarchived     = "unarchived"
 	evSnoozed        = "snoozed"
 	evUnsnoozed      = "unsnoozed"
 	evResolved       = "resolved"
@@ -143,6 +145,17 @@ func logEvent(ctx context.Context, q querier, incidentID int64, evType string, u
 	return err
 }
 
+// logAssignedEvent records an assignment: user_id is the assignee, and the
+// caller who performed it goes in the actor_* columns (migration 018), since
+// user_id cannot hold both.
+func logAssignedEvent(ctx context.Context, q querier, incidentID, assigneeID int64, actorUserID, actorServiceAccountID *int64) error {
+	_, err := q.ExecContext(ctx, `
+		INSERT INTO incident_events (incident_id, type, user_id, actor_user_id, actor_service_account_id, created_at)
+		VALUES ($1, $2, $3, $4, $5, $6)`,
+		incidentID, evAssigned, assigneeID, actorUserID, actorServiceAccountID, time.Now().Unix())
+	return err
+}
+
 // todayUTC is the schedule's day key. The schedule's smallest unit is one UTC day.
 func todayUTC() string {
 	return time.Now().UTC().Format("2006-01-02")