Re-enable shard allocation correction

[rumaxr]

Use 'persistent' instead of 'transient'

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[elasticmachine]

Pinging @elastic/es-core-infra

[danielmitterdorfer]

Thank you for your interest and your contribution to Elasticsearch. I noticed that this change has been made already a while ago in #29671 but that commit never made it to the 6.0 branch. I've cherry-picked it now in 728013a so this changes are also on 6.0 now and therefore I hope you don't mind that I'll close this PR.