spread env into process.env

in the _worker.js template take the provided env and
spread its values into the global process.env so that
bindings can be accessed in the Next.js application

.changeset/young-coins-appear.md

@@ -0,0 +1,5 @@
+---
+"@cloudflare/next-on-pages": minor
+---
+
+Environment variables and bindings are now available on `process.env` from within your SSR'd pages/API handlers!

templates/_worker.js/index.ts

@@ -128,6 +128,8 @@ declare const __MIDDLEWARE__: EdgeFunctions;
 
 export default {
   async fetch(request, env, context) {
+    globalThis.process.env = { ...globalThis.process.env, ...env };
+
     const { pathname } = new URL(request.url);
     const routes = routesMatcher({ request }, __CONFIG__.routes);