Handle metadata fix edge case: GitHub request URL too long error

For papers with large amounts of metadata, the GET URL string is beyond GitHub's limit for the issue template. We need to head this off and give people instructions on how to deal with it manually, so they don't lose a bunch of work after manipulating the dialog.

> I think we should figure out the limit, set the threshold short of that, and guide the user through the following:
> * Present the JSON data structure in the dialog, along with a copy to clipboard button
> * Give them a link to the issue template, with just a minimal URL string
> * Instruct them to manually paste the complete JSON block into the issue

_Originally posted by @mjpost in https://github.com/acl-org/acl-anthology/issues/4374#issuecomment-2906861219_