Harden REGEX for the issue URL (on lookup issue page)

We might also want to consider adding something into the ManageIssuePage itself that validates and displays an error or something if the path doesn't match?

The following discussion from !1317 (merged) should be addressed:

• @leetickett-gitlab started a discussion: (+1 comment)

  • hardened the regex for the issue URL (we should maybe harden the one on the other page in a follow-up merge request- that might resolve #198 (closed))