Allow for redirects to anchors

[shainaraskas]

We have merged some pages. To help people to get to comparable information as accurately as possible between the old and new system, we might want to direct them to a specific anchor on a new page. We could consider allowing for redirects directly to anchors to support this.

Right now, many of our pages are too small, which makes for bad SEO. we want to be able to merge pages where it improves the user experience / seo, and makes sense to do so conceptually. Maintaining redirects directly to content included on the page will make this process easier.

[bmorelli25]

Partially solved by #556. Internal docs here.

Still to be added: Implement actual redirects (not just link resolution between content sets).