[c-lightning] Towards an autopilot

[ZmnSCPxj]

Good morning c-lightningers,

Another useful channel-level statistic: `msatoshi_to_us_min`.  This is the lowest value of `msatoshi_to_us` that a channel ever reached.  This is useful to judge how much risk we have that our counterparty will steal the funds.  The counterparty, obviously, would prefer to steal the state where the `msatoshi_to_us` is lowest.  So keeping track of `msatoshi_to_us - msatoshi_to_us_min` (maximum stealable from us) versus `msatoshi_total - msatoshi_to_us` (money counterparty already has onchannel, and which counterparty is risking if they attempt to steal) would let us consider to close a channel if the stealable amount becomes too large compared to the counterparty risked amount.

This is useful for an autopilot algo to propose closing channels that have a risk.

Regards,
ZmnSCPxj