Issues found during https://github.com/kubeflow/website/pull/3737

[hbelmiro]

These issues were found during #3737.

• Rethink the "Build a More Advanced ML Pipeline" guide pipelines#11639
• Create a feature map to understand what are the features that need documentation pipelines#11638
• Move /pipelines/legacy-v1/overview/multi-user/ -> /pipelines/operator-guides/multi-user/ #3749
• Move (and update) Pipelines pages from Legacy (v1) to Pipelines root pipelines#11637
• Add "Out of date" warnings to all Pipelines v1 docs #3751
• Create a V2 version of "Manipulate Kubernetes Resources as Part of a Pipeline" pipelines#11636
• Fix broken links to /docs/components/pipelines/sdk-v2 and its children. #3756
• Update the "Pipeline Root" concept page and add a new "Configure Pipeline Root" page under "Operator Guide" pipelines#11635
• Fix 404s in _redirects #3761

/area pipelines

[hbelmiro]

I'm adding the issues to #3712. This epic is not needed.