And add redirects
Part of the following issue:
- https://github.com/fleetdm/fleet/issues/41419
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Chores**
* Updated legacy documentation redirects so older `/docs/using-fleet/*`
and `/guides/*` URLs now point to the correct current guide and report
destinations (301), including fixes for Fleet UI, learn-how-to-use, and
report/library links.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Eric <eashaw@sailsjs.com>
