spindle: fix rbac domain prefix

Signed-off-by: oppiliappan <[e-mail]>

spindle/server.go

···
 		cfg: cfg,
 	}
 
-	err = e.AddKnot(rbacDomain)
+	err = e.AddSpindle(rbacDomain)
 	if err != nil {
 		return fmt.Errorf("failed to set rbac domain: %w", err)
 	}