feat: add ga4 plugin (#654)

I didn't want to block you anymore, so I've created the PR as is.
Although I did just recently make a change to no longer hardcode the
fresh version in my plugin, and it no longer references ga4 main. (In
the unlikely event that anyone updates the project, we're now safe.)

I will try to finish the tests later this week, and then I think it's
time for a `0.1.0` release, since I suppose not a lot will change after
the tests are done.

---------

Co-authored-by: Asher Gomez <[email protected]>

README.md

@@ -269,6 +269,14 @@ git rev-parse HEAD
    [set up your Stripe branding](https://dashboard.stripe.com/settings/branding)
    to customize the look and feel of your Stripe checkout page.
 
+### Google Analytics (Optional)
+
+Set `GA4_MEASUREMENT_ID` in your production environment to enable Google
+Analytics.
+
+> Note: it is not recommended to set this locally, otherwise your tests and
+> debugging requests will be logged.
+
 ## REST API Reference
 
 ### `GET /api/items`

fresh.config.ts

@@ -6,14 +6,16 @@ import errorHandling from "./plugins/error_handling.ts";
 import securityHeaders from "./plugins/security_headers.ts";
 import welcomePlugin from "./plugins/welcome.ts";
 import type { FreshConfig } from "$fresh/server.ts";
+import { ga4Plugin } from "https://deno.land/x/[email protected]/mod.ts";
 
 export default {
   plugins: [
+    ga4Plugin(),
     welcomePlugin,
     kvOAuthPlugin,
     sessionPlugin,
     tailwind(),
     errorHandling,
     securityHeaders,
   ],
-} as FreshConfig;
+} satisfies FreshConfig;