[triggers] add command to wait for a chain fee rate

[alexbosworth]

this command will wait for blocks or mempool, analyze the fee rate against a criteria, then either continue with success if the fee rate is lower or continue waiting if the fee rate is higher

add this in a new non-interactive mode

bos triggers wait --condition "chain_fee_rate(6) < 50"

this will wait for the chain fee rate for 6 block confirmation to be below 50 sat/vbyte, then terminate

this would be used for things where you could chain two commands together, like wait for chain fees to go below x and then initiate a channel open