Add an option - that, if enabled, will delete all leading slashes from gotwo "src" items

It's a problem inherited from Drupal (or apache mod rewrite to be more precise). I don't think your proposal is the correct way to solve this. We can validate against this on submit (before we process the gotwo urls) and throw an error on submit. We need to see how path.module or pathauto.module handle this problem.

Marking as duplicate of #86316: Trailing slash in url give "page not found"

If we prevent trailing slash on submit, then there will be no need to scan through the entire go list again!