[CE] Backport SAML unlink changes: UrlBlocker#ascii_only

Commits

commit: 72c00594070dfd1a778c2e03ff400b478e6c3774
Author: James Edwards-Jones <jedwardsjones@gitlab.com>
Date:   Wed Dec 5 20:14:09 2018 +0000

    Allow URLs to be validated as ascii_only
    
    Restricts unicode characters and IDNA deviations
    which could be used in a phishing attack

Related

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8295

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer