Added logout API

lib/bigcommerce/api/customers/handlers/logout.ts

@@ -0,0 +1,16 @@
+import { LogoutHandlers } from '../logout'
+
+const logoutHandler: LogoutHandlers['logout'] = async ({
+  res,
+  body: { redirectTo },
+  config,
+}) => {
+  // Only allow redirects to a relative URL
+  if (redirectTo?.startsWith('/')) {
+    res.redirect(redirectTo)
+  } else {
+    res.status(200).json({ data: null })
+  }
+}
+
+export default logoutHandler