cli: add max_cltv, max_fee_millionths, fee_cutoff_msat parameters to lnpay

[f321x]

Adds max_cltv, max_fee_millionths and fee_cutoff_msat parameters to the lnpay cli command which allow to specify a custom PaymentFeeBudget for the lnpay payment. Allowing to specify a these parameters can be useful for usecases like #10056.

Closes #10056

[supertestnet]

I added a comment to the referenced issue here and I hereby copy my comment:

I noticed in your PR that you add some code concerning how the max fee is calculated; it may be useful to let the user override that via an argument in lnpay. For example, if I make a proxy service, perhaps I will charge a flat fee of 50 sats to users; I would like to pass an argument to lnpay with something like max_fee = 49, that way it won't pay more than 49 sats to route the payment, even if my electrum settings would otherwise allow it. That way, my proxy server profits from every outgoing payment.

[f321x]

I have added max_fee_millionths and fee_cutoff_msat parameters to lnpay in 2241015. Now it is possible to fully specify the PaymentFeeBudget with arguments to lnpay.