Page Redirect UI: Example and Outcome is misleading for external URLs

[stevepiercy]

Details

From: #4008 (comment)

When creating a Page Redirect to an external URL, there are two issues:

1. The Example for To URL: does not indicate that a fully qualified URL is acceptable.
2. The Outcome preview of the redirect is misleading. It prefixes /$lang/$version/ to the external URL, potentially misleading the user to think that Page Redirects work only for internal RTD URLs.

Outcome: /$lang/$version/docs/pyramid.html -> /$lang/$version/https://trypyramid.com/resources.html

Upon clicking the Add button, the redirect works. It's just the lead up in the UI that is the problem.

Expected Results

1. The Help should indicate that any fully qualified URL, or a RTD-relative filepath, is acceptable.
2. The UI should recognize the presence of a protocol and/or external domain name in the To URL: input and exclude the /$lang/$version/ prefix.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.