Set optional checkout.session.url (#4569)

* Set optional checkout.session.url

* Lint

* Edit .env.example

* Vale CI

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Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-front/src/config/index.ts

@@ -27,4 +27,4 @@ const getDefaultUrl = () => {
 export const REACT_APP_SERVER_BASE_URL =
   window._env_?.REACT_APP_SERVER_BASE_URL ||
   process.env.REACT_APP_SERVER_BASE_URL ||
-  getDefaultUrl();
+  getDefaultUrl();