Add config for objectId size (#3950)

* Add objectId config property, default to 10

* Update Config constructor

* Add test for backwards compatibility when changing objectId size

src/cryptoUtils.js

@@ -35,9 +35,8 @@ export function randomString(size: number): string {
 }
 
 // Returns a new random alphanumeric string suitable for object ID.
-export function newObjectId(): string {
-  //TODO: increase length to better protect against collisions.
-  return randomString(10);
+export function newObjectId(size: number = 10): string {
+  return randomString(size);
 }
 
 // Returns a new random hex string suitable for secure tokens.