[feature]: allow configuring upfront shutdown address in `lnd.conf`

[yyforyongyu]

As of today, a funder can easily specify the upfront shutdown address via openchannel. A fundee, however, needs to set up a channel acceptor to specify a custom address. This can be cumbersome, especially in the case where a remote signer is used for a hot-cold wallet setup. We could instead config this shutdown address in lnd.conf,

• [ ] add a new config value upfront-shutdown-address and use it when opening and accepting channels.
• [ ] it can be overwritten by the value specified in openchannel and/or channel acceptor.

Going with this approach does decrease the level of privacy as all the funds now go to the same cold wallet address. A better approach is to stick to the current setup - always derive a new cold wallet address when opening or accepting a channel, however this is up to the user to decide.

[blckbx]

Going with this approach does decrease the level of privacy as all the funds now go to the same cold wallet address. A better approach is to stick to the current setup - always derive a new cold wallet address when opening or accepting a channel, however this is up to the user to decide.

As a middle way, could we provide an array of addresses that are cycled through? Are these addresses also used in force-closes?

[theedtron]

Can I jump on this?

[raehat]

@theedtron, if you're currently not working on this, can I take this?

[theedtron]

@raehat still planning to work on it.