Issue

The handling of fee limits is inconsistent on different api endpoints.
The lightning-pay api endpoint exposes maxfee, maxfeepercent and exemptfee fee as parameters. (https://docs.corelightning.org/reference/lightning-pay)
The lightning-keysend api enpoint only exposes maxfeepercent and exemptfee. (https://docs.corelightning.org/reference/lightning-keysend)

Please add maxfee to lightning-keysend to simplify and unify api handling.