docs: new and shiny storage limit docs

[woodruffw]

This is my attempt to scaffold out a clean segue from the existing help.html to the newer mkdocs-managed user documentation, using #17702 as a testcase.

Key changes:

• There's a new request.user_docs_url request method that makes it easy to route to user documentation pages, including specific anchors.
• I've added /project-management/storage-limits/ with most of the file/project storage limit content from help.html, along with additional context/rendering niceties/screenshots.
• I've added /project-management/yanking/ with the yanking content from help.html, along with a short user tutorial on yanking releases.
• I've removed the original yanking and file/project storage limit sections from help.html and changed the endpoints/views that linked it to link to the new docs page instead.

Some open questions:

• Is this a good idea at all? I think the newer user docs are easier to iterate on, but I don't know if it's worth the complexity of the new user_docs_url request method 😅
• Does /project-management/ make sense as a hierarchy for these docs? Or should this be just a top level /storage-limits/ or similar, or something different?

See #17702.

Closes #9013.

[woodruffw]

For reference, this is what the new storage limits docs look like with this PR:

[woodruffw]

NB: This ensures that local deployments link to the local user docs build, rather than docs.pypi.org (which is otherwise the default).

[di]

@woodruffw FYI, you need to rebuild translations here.

[woodruffw]

@woodruffw FYI, you need to rebuild translations here.

Done!