Docs: Add some details to the User Defined Redirects (#7894)
Docs: Add some details to the User Defined Redirects (#7894)

- Move the "Implementation" section further up as a note, so that it's
  more visible (I missed it myself and spent some time trying to test
  redirects on 200 which do not work). Remove part about not running
  logic as it's no longer accurate.
- Add mentions to the use case of setting Exact Redirects to have
  Page Redirects but applied only to a specific version. It's common
  to move pages only in the `latest` branch/future stable branches,
  without doing the change in older branches.
- The button to confirm a redirect is now named "Add".

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