Switch billing provider from Stripe to Lemon Squeezy

Changed the billing provider in the `.env.development` file from Stripe to Lemon Squeezy. This requires adaptations at many levels: at the web app to load Lemon Squeezy's script in the checkout process, at the billing gateway to handle Lemon Squeezy calls, and in the database to reflect the current billing provider. The checkout process is now done using Lemon Squeezy Sessions and its billing strategy was adjusted accordingly. Billing-related components and services were also updated.

packages/billing/lemon-squeezy/src/components/lemon-squeezy-embedded-checkout.tsx

@@ -1,3 +1,7 @@
+'use client';
+
+import { useEffect } from 'react';
+
 interface LemonSqueezyWindow extends Window {
   createLemonSqueezy: () => void;
   LemonSqueezy: {
@@ -14,16 +18,24 @@ interface LemonSqueezyWindow extends Window {
 }
 
 export function LemonSqueezyEmbeddedCheckout(props: { checkoutToken: string }) {
-  return (
-    <script
-      src="https://app.lemonsqueezy.com/js/lemon.js"
-      defer
-      onLoad={() => {
-        const win = window as unknown as LemonSqueezyWindow;
+  useLoadScript(props.checkoutToken);
 
-        win.createLemonSqueezy();
-        win.LemonSqueezy.Url.Open(props.checkoutToken);
-      }}
-    ></script>
-  );
+  return null;
+}
+
+function useLoadScript(checkoutToken: string) {
+  useEffect(() => {
+    const script = document.createElement('script');
+
+    script.src = 'https://app.lemonsqueezy.com/js/lemon.js';
+
+    script.onload = () => {
+      const win = window as unknown as LemonSqueezyWindow;
+
+      win.createLemonSqueezy();
+      win.LemonSqueezy.Url.Open(checkoutToken);
+    };
+
+    document.body.appendChild(script);
+  }, [checkoutToken]);
 }