[Docs RFC] Remove MST migration guides, point users to the migration section

[billy-the-fish]

• Add the info in the MST migration guides to the migration section.
• Replace migration docs with redirects to new docs
  • https://docs.timescale.com/migrate/latest/
  • https://docs.timescale.com/mst/latest/migrate-to-mst/
• Add navigation links in the MST docs.