Add an "history completeness check"

related to "hole" problems (see swh/devel/experiments/swh-db-audit#3656 (moved), swh-loader-git#3655)

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Migrated from T4136 (view on Phabricator)

mentioned in merge request swh-scrubber!17 (closed)

assigned to @vlorentz

marked this issue as related to swh/meta#3841

added Storage manager priority:Normal labels

closed