[feature]: FundChannel: allow setting local_funding_amount

[ZZiigguurraatt]

Allow setting local_funding_amount with FundChannel. Currently we have no way to change the amount of sats that are in a taproot assets channel.

We can change push_sat, but if you try to push too much, you can get an error amount pushed to remote peer for initial state must be below the local funding amount.

We should be able to use a taproot assets channel for both taproot assets and sats. It increases the usefulness of the channel and reduces the need for additional on chain transactions.

Also, right now, when testing with lots of payments, we can quickly deplete the sats in the channel because of #888 . If we are not able to change the amount of sats in a channel and push as much as we want to the other side when opening, we have to do extra bookeeping to make sure we have enough sats in our channel to keep making payments.