Frozen ledgers should propagate to new nodes in the pool

[esplinr]

According to HIPE 0162 Frozen Ledgers, frozen ledgers do not participate in catch up. New validators added to a pool with frozen ledgers do not receive the history of the frozen ledgers.

Theoretically, someone could freeze a ledger with history and lose that history due to evolution of the validator pool, which would prevent them from being able to perform a third party audit of the ledger history. This can be avoided by propagating the history of frozen ledgers to new nodes in the pool.