Allow to configure what party pays for the on-chain transaction fee on force closure

[luckysori]

10101 creates inbound channels with its users. The fees for force-closing the ln-channel is always paid by the initiator, but for the dlc channel its always 50/50 with the offering party paying the extra sat if the fees are not mod 2.

We need a way of configuring that 50/50 split to allow for a similar approach like a vanilla lightning channel. Ideally only the initiator pays for any fees related to onchain-transactions for force-closing a channel. Thus to de-incentivise force closures.

Additionally we might want to consider always letting the user pay for on-chain transaction fees when force-closing a dlc channel as the user should come online again to either collab close or "rollover" the position.

@Tibo-lg mentioned that this might be a good opportunity to incorporate recent changes from rust-bitcoin in terms of fee calculation.

// edit: @holzeis added additional description