Try to improve build speed with worker threads and some other tweaks (#1255)

* Set cpu=1 in next.config.js

* Try to improve build speed a little using worker threads.

* Make this run on prod only

Author: sfc-gh-tteixeira

next.config.js

@@ -4,7 +4,9 @@ const PROD_OPTIMIZATIONS = IS_DEV
   ? {}
   : {
       experimental: {
-        cpus: 1,
+        workerThreads: true,
+        cpus: 2,
+        sharedPool: true,
       },
     };