Storage Replication refactoring

[J-Loudet]

Describe the feature

As described in #886 the behavior of the Aligner Queryable is not particularly optimized, to quote the changes made in the pull request:

1. Incrementally replies with digest replies in order to avoid queries timing out w/o sending any data, especially in the case of very outdated storages.
2. Replace the unbounded queue for digests with a bounded queue to prevent infinitely growing digest queues when digest updates take a long time.

Similarly, #884 removes quite a few unwrap() that have their invariant violated.

This strongly indicates that a deep refactoring of the Storage Replication is needed.

This issue will serve as a central tracking point for Replication-related items.