Track rollbacks

[wolf31o2]

Track the rollback state. On initial start, we shouldn't emit a log or metric for a rollback. Otherwise, the rollback state will effect logging and metrics.

• Track if we're starting up and "do nothing" (no logs/metrics) on the initial start/rollback
• When a rollback happens, set state to show we're migrating to a fork
• On the next roll forward, we should emit a log that we've switched to the new fork
• Increment Fork metric (cardano_node_metrics_forks_int)

This behavior should try to mimic the Haskell node's logging and metrics.