Add docs for MoveTables auto increment handling

[mattlord]

This documents the work done in https://github.com/vitessio/vitess/pull/16860

Pages updated:

• https://deploy-preview-1859--vitess.netlify.app/docs/21.0/reference/vreplication/movetables
• https://deploy-preview-1859--vitess.netlify.app/docs/21.0/reference/programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_create/
• https://deploy-preview-1859--vitess.netlify.app/docs/21.0/reference/programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_switchtraffic/

[netlify[bot]]

✅ Deploy Preview for vitess ready!

Name	Link
🔨 Latest commit	921a2f10b9c8edf7d16d4e135e4763dd9681ac6c
🔍 Latest deploy log	https://app.netlify.com/sites/vitess/deploys/66ff5b3cf6e0b00008a427ce
😎 Deploy Preview	https://deploy-preview-1859--vitess.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.