multi: add new config option BudgetConfig and NoDeadlineConfTarget

This commit adds a new group config `BudgetConfig` to allow users
specifying their own preference when sweeping outputs. And a new config
option `NoDeadlineConfTarget` is added in case the user wants to use a
different "lazy" conf target.

sample-lnd.conf

@@ -1622,6 +1622,57 @@
 ; causing HTLCs to expire hence potentially losing funds.
 ; sweeper.maxfeerate=1000
 
+; The conf target to use when sweeping non-time-sensitive outputs. This is
+; useful for sweeping outputs that are not time-sensitive, and can be swept at
+; a lower fee rate.
+; sweeper.nodeadlineconftarget=1008
+
+
+; An optional config group that's used for the automatic sweep fee estimation.
+; The Budget config gives options to limits ones fee exposure when sweeping
+; unilateral close outputs and the fee rate calculated from budgets is capped
+; at sweeper.maxfeerate. Check the budget config options for more details.
+; sweeper.budget=
+
+[sweeper.budget]
+
+; The amount in satoshis to allocate as the budget to pay fees when sweeping
+; the to_local output. If set, the budget calculated using the ratio (if set)
+; will be capped at this value.
+; sweeper.budget.tolocal=
+
+; The ratio of the value in to_local output to allocate as the budget to pay
+; fees when sweeping it.
+; sweeper.budget.tolocalratio=0.5
+
+; The amount in satoshis to allocate as the budget to pay fees when CPFPing a
+; force close tx using the anchor output. If set, the budget calculated using
+; the ratio (if set) will be capped at this value.
+; sweeper.budget.anchorcpfp=
+
+; The ratio of a special value to allocate as the budget to pay fees when 
+; CPFPing a force close tx using the anchor output. The special value is the
+; sum of all time-sensitive HTLCs on this commitment subtracted by their
+; budgets.
+; sweeper.budget.anchorcpfpratio=0.5
+
+; The amount in satoshis to allocate as the budget to pay fees when sweeping a
+; time-sensitive (first-level) HTLC. If set, the budget calculated using the
+; ratio (if set) will be capped at this value.
+; sweeper.budget.deadlinehtlc=
+
+; The ratio of the value in a time-sensitive (first-level) HTLC to allocate as
+; the budget to pay fees when sweeping it.
+; sweeper.budget.deadlinehtlcratio=0.5
+
+; The amount in satoshis to allocate as the budget to pay fees when sweeping a
+; non-time-sensitive (second-level) HTLC. If set, the budget calculated using
+; the ratio (if set) will be capped at this value.
+; sweeper.budget.nodeadlinehtlc=
+
+; The ratio of the value in a non-time-sensitive (second-level) HTLC to
+; allocate as the budget to pay fees when sweeping it.
+; sweeper.budget.nodeadlinehtlcratio=0.5
 
 [htlcswitch]