chore: allow e2e port to be defined by env vars (#16285)

Port number is currently hardcoded to 3000, this makes it so it defaults
back to 3000 but you can override it via env vars. Helps when running
lots of e2es in parallel with various agents by providing
predictability.

Author: paulpopus

test/__helpers/shared/initPayloadE2ENoConfig.ts

@@ -26,7 +26,10 @@ export async function initPayloadE2ENoConfig<T extends GeneratedTypes<T>>({
 }: Args): Promise<Result<T>> {
   const testSuiteName = path.basename(dirname)
 
-  const port = 3000
+  // Default to 3000 if PORT is not set, but allow it to be overridden by the environment variable
+  const defaultPort = 3000
+
+  const port = process.env.PORT ? Number(process.env.PORT) : defaultPort
   process.env.PORT = String(port)
   process.env.PAYLOAD_CI_DEPENDENCY_CHECKER = 'true'
 
@@ -51,7 +54,7 @@ export async function initPayloadE2ENoConfig<T extends GeneratedTypes<T>>({
         if (code === 0) {
           res()
         }
-        rej()
+        rej(new Error('closed with code ' + code))
       })
     })
   }