br: add use constraint with TiCDC and Drainer (#3839)
br: add use constraint with TiCDC and Drainer (#3839)

* br: add use constraint with CDC and drainer

* fix errors

* Apply suggestions from code review

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>

* Update br/backup-and-restore-faq.md

* Update br/backup-and-restore-faq.md

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs,pingcap/docs,pingcap/docs