Co-authored-by: Joost Jager <joost.jager@gmail.com>

Exclusive group is a static property that doesn't need to be updated.
Requiring the exclusive group to be passed into UpdateParams creates a
burden for the caller to make sure they supply the existing group.

This change will be beneficial for users that bump anchor sweeps that
have exclusive groups set.

Prior to this change, the trigger height for closed channels was set to
the current best block height. As this height is in some cases used as a
height hint, the spend may have been missed.

Allows unit testing of the channel arbitrator with fewer dependencies.
This is a preparation for the addition of anchor sweeping.

Relay fee is needed later to sweep anchors at the minimum fee rate.

Start anchor sweep attempts immediately after the commitment transaction
has been published. This makes the anchor known to the sweeper and
allows the user to bump the fee on it to get their commitment
transaction confirmed in case the fee committed too is insufficient for
timely confirmation.

Preparation for the anchor resolver which does not have persistent
state.

Preparation for anchor resolver. The recovered anchor amount should
still be included in the pending channel report even after it has been
resolved.

This also fixes an existing bug that in some cases caused the recovered
amount from an htlc resolver not to be included in the total.

Sweeping anchors and being able to bump the fee was already added in a
previous commit. This commit extends anchor sweeping with an anchor
resolver object that becomes active after the commitment tx confirms.
At that point, the anchors do not serve the purpose of getting the
commitment tranaction confirmed anymore. It is however still possible to
reclaim some of their value if using a low fee rate.

To make it easier to determine which pending sweep to bump in order to
get your anchor commitment tx confirmed.

This command allows users to easily bump the fee on their unconfirmed
closing transactions.