Default enable invalid metadata deletion in Praefect

Praefect has a metadata verifier that checks whether the replicas recorded in the database actually exist. For now, it has only logged and gathered metrics on invalid metadata records by default. The verifier also supports deleting invalid metadata which clean up the stale records and allows Praefect to realize the replicas are missing and trigger replication. This functionality has been disabled in the past as renames racing with the verificaton could cause data loss. Since 15.3, Praefect has been using Praefect generate replica paths and not performing any more renames on disk. Given this, there are no more races that we know of, so we can default enable the invalid metadata deletion.

Changelog: changed

Closes #4429 (closed)
Documentation gitlab!110661 (merged)

Praefect generated paths were default enabled in !4809 (merged). Enabling this functionality stopped renames from being scheduled. !4941 (merged) removed the feature flag so everyone has the pre-requisite set.