Figure out what to do with 'misordered' directories in Cassandra

In postgresql, we stored the list of entries in an array (with an arbitrary order); while in Cassandra it is in a table, sorted by name.

Most of the time it does not matter; but some Git directories are not in the right order, which means they cannot be round-tripped through Cassandra. We need to do something about these.

(Found while working on swh/devel/experiments/swh-db-audit#75 (moved))

Possibly a duplicate of #3595 (closed)

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Migrated from T3586 (view on Phabricator)