refactor command package to remove globals and add dependency injection

cmd/syft/cli/eventloop/signals.go

@@ -0,0 +1,20 @@
+package eventloop
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+func SetupSignals() <-chan os.Signal {
+	c := make(chan os.Signal, 1) // Note: A buffered channel is recommended for this; see https://golang.org/pkg/os/signal/#Notify
+
+	interruptions := []os.Signal{
+		syscall.SIGINT,
+		syscall.SIGTERM,
+	}
+
+	signal.Notify(c, interruptions...)
+
+	return c
+}