wallet: add coin selection parameter `add_excess_to_recipient_position` for changeless txs with excess that would be added to fees

This PR replaces draft PR 29442 as a simpler alternative that only adds two new coin selection parameters: add_excess_to_recipient_position and max_excess.

motivation

A changeless transaction may select inputs with excess value over what is needed to reach the desired fee rate and output targets. Currently that excess value is considered waste and burned as fees. In some situations you may prefer to add any excess value to an output you control. When fees are high the cost of adding a change output increases and so does the amount of potential excess value spent as fees. One example of a situation where excess value should be added to the output amount is when splicing in value to a Lightning channel because the excess value is retained off-chain.