unable to use a CDN url longer than 255 chars
As part of the ISS feature, users set the CDN url to a different hostname and path. Occasionally, this path might be greater than 255 char.
Katello needs to be able to support >255 char CDN urls.
Fixes #14329 - allow 1024 char CDN urls
Previously, the CDN url was limited to 255 char. This db migration updates it
to 1024 char.