Backport: Revert "Remove legacy project routes"

This reverts merge request Remove legacy project routes (!120720 - merged)

We removed some project route redirects that had been deprecated for some time. We had a few reports on slack that certain links weren't working anymore so we have decided to revert the change and come up with a better way to communicate the deprecations.

Possible regression caused by removed routes (#412435 - closed)

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