[Feature Flag] Rollout of `block_issue_repositioning`

:block_issue_repositioning has been added on !60141 (merged) to prevent issue manual reordering or rebalance when big project imports are happening.

This is a temporary solution to avoid put database under stress and prevent possible incidents as gitlab-com/gl-infra/production#4321 (closed).

We can remove this as soon as the root cause of the performance issue when importing big projects gets resolved.