refactor cli vpn config (#46)

* refactor cli vpn config

Co-authored-by: katexochen <49727155+katexochen@users.noreply.github.com>

cli/cmd/vpnconfig_test.go

@@ -0,0 +1,25 @@
+package cmd
+
+import wgquick "github.com/nmiculinic/wg-quick-go"
+
+type stubVPNHandler struct {
+	configured bool
+	marshalRes string
+
+	createErr  error
+	applyErr   error
+	marshalErr error
+}
+
+func (c *stubVPNHandler) Create(coordinatorPubKey string, coordinatorPubIP string, clientPrivKey string, clientVPNIP string, mtu int) (*wgquick.Config, error) {
+	return &wgquick.Config{}, c.createErr
+}
+
+func (c *stubVPNHandler) Apply(*wgquick.Config) error {
+	c.configured = true
+	return c.applyErr
+}
+
+func (c *stubVPNHandler) Marshal(*wgquick.Config) ([]byte, error) {
+	return []byte(c.marshalRes), c.marshalErr
+}