fix metadata base to set proper canonical urls (#5613)

fixes: DASH-492

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---

## PR-Codex overview
This PR focuses on updating the `metadata` in the `layout.tsx` file and modifying the sitemap configuration in `next-sitemap.config.js` to improve SEO and access control based on the environment.

### Detailed summary
- In `layout.tsx`:
  - Added `metadataBase` with URL `https://thirdweb.com`.
  - Introduced `alternates` with a `canonical` path set to `"./"`.

- In `next-sitemap.config.js`:
  - Updated access rules:
    - Allowed access if `VERCEL_ENV` is `"production"`.
    - Disallowed access to all if not in production, except for specific paths (`/team` and `/team/*`).

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Author: jnsdls

apps/dashboard/next-sitemap.config.js

@@ -48,10 +48,14 @@ module.exports = {
     policies: [
       {
         userAgent: "*",
-        [process.env.VERCEL_ENV !== "preview" &&
-        process.env.VERCEL_ENV !== "development"
-          ? "allow"
-          : "disallow"]: "/",
+        // allow all if production
+        allow: process.env.VERCEL_ENV === "production" ? ["/"] : [],
+        // disallow all if not production
+        disallow:
+          process.env.VERCEL_ENV !== "production"
+            ? ["/"]
+            : // disallow `/team` and `/team/*` if production
+              ["/team", "/team/*"],
       },
     ],
   },

apps/dashboard/src/app/layout.tsx

@@ -17,6 +17,10 @@ const fontSans = Inter({
 });
 
 export const metadata: Metadata = {
+  metadataBase: new URL("https://thirdweb.com"),
+  alternates: {
+    canonical: "./",
+  },
   title: "thirdweb: The complete web3 development platform",
   description:
     "Build web3 apps easily with thirdweb's powerful SDKs, audited smart contracts, and developer tools—for Ethereum & 700+ EVM chains. Try now.",