#6101 Let users define objectId (#6177)

* #6101 Let users define objectId

* Add `allowCustomObjectId` to PS Option

* Add checking in objectId creation

* Add test

* Update docs

* Update definition

* Change default to false

* throw on empty, null, undefined

* better tests

* unused async

* removed comment

* retain comment

* Linting fix according to contributing spec.

src/Options/Definitions.js

@@ -17,6 +17,12 @@ module.exports.ParseServerOptions = {
     action: parsers.booleanParser,
     default: true,
   },
+  allowCustomObjectId: {
+    env: 'PARSE_SERVER_ALLOW_CUSTOM_OBJECT_ID',
+    help: 'Enable (or disable) custom objectId, defaults to false',
+    action: parsers.booleanParser,
+    default: false,
+  },
   allowHeaders: {
     env: 'PARSE_SERVER_ALLOW_HEADERS',
     help: 'Add headers to Access-Control-Allow-Headers',