Allow for user-specified error message to `force_close_with*_broadcasting_txn`

[TheBlueMatt]

We have to send an error message to peers, so we might as well let the user configure it.

[Sharmalm]

Hey @TheBlueMatt can i try this issue?

[TheBlueMatt]

Go for it

[Sharmalm]

Ok,
So in this issue, we have to allow users to send error message while force_close_with*_broadcasting_txn and force_close_without_broadcasting_txn both, right?
To configure custom error message, my approach is to update the parameters of func fn force_close_sending_error(&self, channel_id: &ChannelId, counterparty_node_id: &PublicKey, broadcast: bool, error_message: &str) -> Result<(), APIError> {

[TheBlueMatt]

Sure

[Sharmalm]

I have made Pr #2889 for this issue, please review it.

[TheBlueMatt]

Fixed in #2889.