fix(nextjs): Add sideEffects flag to NextJS SDK (#4216)

We have side effects in `index.server.ts`, so we mark as such in our
package.json.

Author: AbhiPrasad

packages/nextjs/package.json

@@ -87,5 +87,10 @@
         "diagnostics": false
       }
     }
-  }
+  },
+  "sideEffects": [
+    "./dist/index.server.js",
+    "./esm/index.server.js",
+    "./src/index.server.ts"
+  ]
 }