[release-22.0] copy_state: use a mediumblob instead of a smaller varbinary for lastpk (#18852)#18858

nickvanw merged 1 commit intorelease-22.0vitessio/vitess:release-22.0from

backport-18852-to-release-22.0vitessio/vitess:backport-18852-to-release-22.0Copy head branch name to clipboard