Add ability to close channel to specific address

[benthecarman]

Would be nice when cooperatively closing a channel to be able to provide an address to close to. Currently the only parameter that is able to be provided is the closing fee rate.

By default commit_upfront_shutdown_pubkey is set to true, maybe this would need to be reconsidered or instead the user would just need to have that set to false for this to work.

[TheBlueMatt]

You can already do this! As long as commit_upfront_shutdown_pubkey is not set, LDK will only call https://docs.rs/lightning/latest/lightning/chain/keysinterface/trait.SignerProvider.html#tymethod.get_shutdown_scriptpubkey once the shutdown initates, which should do what you want?