sparkles: Boot options (#91)

* ✨ Add grub_options to config

Split post-install into hooks

* 🤖 Adapt test to latest releases

internal/agent/hooks/hook.go

@@ -0,0 +1,24 @@
+package hook
+
+import (
+	config "github.com/c3os-io/c3os/pkg/config"
+)
+
+type Interface interface {
+	Run(c config.Config) error
+}
+
+var All = []Interface{
+	&RunStage{},    // Shells out to stages defined from the container image
+	&GrubOptions{}, // Set custom GRUB options
+	&Lifecycle{},   // Handles poweroff/reboot by config options
+}
+
+func Run(c config.Config, hooks ...Interface) error {
+	for _, h := range hooks {
+		if err := h.Run(c); err != nil {
+			return err
+		}
+	}
+	return nil
+}