feat(cache): add Cache-Control middleware and update .env.example

src/config/cache_control_middleware.ts

@@ -0,0 +1,15 @@
+import type { MiddlewareHandler } from "hono";
+
+// Define middleware to add Cache-Control header
+const cacheControlMiddleware: MiddlewareHandler = async (c, next) => {
+  const sMaxAge = process.env.S_MAXAGE || "60";
+  const staleWhileRevalidate = process.env.STALE_WHILE_REVALIDATE || "30";
+  c.header(
+    "Cache-Control",
+    `s-maxage=${sMaxAge}, stale-while-revalidate=${staleWhileRevalidate}`
+  );
+
+  await next();
+};
+
+export default cacheControlMiddleware;