**Problem:**
We want to allow sitelinks to redirects but only under certain conditions. In detail this means:
* The default behavior stays rejecting of adding of sitelinks that are links to redirected pages
* A sitelink to a redirected pages can be added to an Item if and only if a redirect badge [[ https://www.wikidata.org/wiki/Special:AvailableBadges | (sitelink to redirect (Q70893996), intentional sitelink to redirect (Q70894304)) ]] is added in the same edit
* Adding a redirect badge to an existing redirect sitelink is possible
* removing a redirect badge from a sitelink that points to a redirected page is disallowed
**Context:**
* In T235420 we added badges to indicate sitelinks to redirects but they can't be used because the edits related to them are disallowed
* https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/602422 contains some work in this direction but is probably not the right approach, (per Adam's comment at T235420#6791998) Adam notes: "Looking at the patch lots of the code will end up being reused, but it will need the addition of some checks etc to optionally pass MediaWikiPageNameNormalizer::NOFOLLOW_REDIRECT into the service etc."
**BDD**
GIVEN an Item
AND a page on the client that is a redirect
WHEN adding the page as a sitelink to the Item
AND not adding a redirect badge in the same edit
THEN the edit is rejected
GIVEN an Item
AND a page on the client that is a redirect
WHEN adding the page as a sitelink to the Item
AND adding a redirect badge in the same edit
THEN the sitelink and associated badge are stored
GIVEN an Item
AND a sitelink to a client page
AND the client page is a redirect
WHEN adding a redirect badge to the sitelink
THEN the badge is stored with the sitelink
GIVEN an ITEM
AND a sitelink to a client page
AND the client page is a redirect
WHEN trying to remove the redirect badge from the sitelink
THEN the edit is rejected
**Acceptance criteria:**
* Default behavior remains unchanged
* Sitelinks to redirect pages are accepted if and only if there is a redirect badge attached to them