Addresses ([#229])
This allows effective feerates (PPM) to be computed for earnings and
expenses.
This PR updates the schema automatically. Downgrading to previous
will require manual DB migration (but is possible). Downgrade
commands are in a comment in EarningsTracker.c
Fixes ([#222])
Prior to ElementsProject/lightning@780f32d (`v23.05`) both `fee` and
`fee_msat` were sent for compatibility. The ForwardFeeMonitor was
checking for the presence of the `fee` field before processing the
record. This needed to be updated to `fee_msat`.
