Update next-google-analytics to work with .env files (#16529)

Changes the name of the environment variable to `NEXT_PUBLIC_GA_TRACKING_ID`

packages/next-plugin-google-analytics/package.json

@@ -8,7 +8,7 @@
   "nextjs": {
     "name": "Google Analytics",
     "required-env": [
-      "GA_TRACKING_ID"
+      "NEXT_PUBLIC_GA_TRACKING_ID"
     ]
   },
   "peerDependencies": {

packages/next-plugin-google-analytics/src/document-head-tags-server.js

@@ -5,7 +5,7 @@ export default async function headTags() {
     <>
       <script
         async
-        src={`https://www.googletagmanager.com/gtag/js?id=${process.env.GA_TRACKING_ID}`}
+        src={`https://www.googletagmanager.com/gtag/js?id=${process.env.NEXT_PUBLIC_GA_TRACKING_ID}`}
       />
       <script
         dangerouslySetInnerHTML={{
@@ -13,7 +13,7 @@ export default async function headTags() {
             window.dataLayer = window.dataLayer || [];
             function gtag(){dataLayer.push(arguments);}
             gtag('js', new Date());
-            gtag('config', '${process.env.GA_TRACKING_ID}');
+            gtag('config', '${process.env.NEXT_PUBLIC_GA_TRACKING_ID}');
           `,
         }}
       />

packages/next-plugin-google-analytics/src/on-init-client.js

 export default async function initClient({ router }) {
   router.events.on('routeChangeComplete', (url) => {
     setTimeout(() => {
-      window.gtag('config', process.env.GA_TRACKING_ID, {
+      window.gtag('config', process.env.NEXT_PUBLIC_GA_TRACKING_ID, {
         page_location: url,
         page_title: document.title,
       })