Enable installing app as pwa

app/javascript/custom/companion.js

@@ -0,0 +1,11 @@
+if (navigator.serviceWorker) {
+  navigator.serviceWorker
+    .register("/service-worker.js", { scope: "/" })
+    .then(() => navigator.serviceWorker.ready)
+    .then((registration) => {
+      if ("SyncManager" in window) {
+        registration.sync.register("sync-forms");
+      }
+    })
+    .then(() => console.log("[Companion]", "Service worker registered!"));
+}