This commit re-adds the LocalBalance and RemoteBalance fields to the
RevocationLog. The channeldb/migration30 is also adjusted so that anyone
who has not yet run the optional migration will not lose these fields if
they run the migration after this commit.
The reason for re-adding these fields is that they are needed if we want
to reconstruct all the info of the lnwallet.BreachRetribution without
having access to the breach spend transaction. In most cases we would
have access to the spend tx since we would see it on-chain at which time
we would want to reconstruct the retribution info. However, for the
watchtower subsystem, we sometimes want to construct the retribution
info withouth having access to the spend transaction.
A user can use the `--no-rev-log-amt-data` flag to opt-out of storing
these amount fields.
Define a MigrationConfig interface that should be used to pass the
config of an optional migration function. An implementation of this
interface is added for migration30 (the only current optional
migration).
