[feature]: add `inbound_fee_rate` as an option to `updatechanpolicy`

[AndySchroder]

We have fee_rate and fee_rate_ppm in updatechanpolicy We also have inbound_fee_rate_ppm but we do not have inbound_fee_rate. Please add inbound_fee_rate for consistency.

[Roasbeef]

We have both fields, but perhaps the naming is unexpected -- base_fee_msat is the base fee: https://lightning.engineering/api-docs/api/lnd/lightning/update-channel-policy#lnrpcinboundfee

[hieblmi]

I think @AndySchroder means to have added the lncli updatechanpolicy --inbound_fee_rate cli option, which we have for the outbound fees.

[AndySchroder]

I think @AndySchroder means to have added the lncli updatechanpolicy --inbound_fee_rate cli option, which we have for the outbound fees.

Yes, I'd like to be able to use the same unit multiplier for setting both inbound and outbound fees for both the base fee and the fee rate. It's very confusing to have to use different unit multipliers for inbound and outbound fees.