Fix domain level redirects

What does this MR do?

Browsing \google.com automatically resolves it to google.com. Thus, adding a /\domain.name.com in _redirects file would redirect to domain.name.com. We do not allow domain-level redirects at all. This MR fixes that.

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Steps to verify the change

1. Add a _redirects file to the public folder of a plain-html pages repo.

/test-boo/test1.html /test-boo/index.html 301
/test-boo/test2.html /test-boo/index.html 302
/test-boo/test3.html /test-boo/boo.html 301
/test-boo/test4.html /test-boo/boo.html 302
/test-boo/test5.html /test-boo/index.html 301
/test-boo/test6.html /test-boo/index.html 302
/test-boo/test7.html /test-boo/boo.html 301
/test-boo/test8.html /test-boo/boo.html 302
/test-boo/test9.html /\www.google.com 301
/test-boo/test10.html /\www.google.com 302

2. Start Pages server and browse http://your-group.pages.gdk.test:3010/your-project/_redirects
3. Validate that it is showing the last 2 rules as invalid

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TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines