feature: use +100 staging bit for taproot channels

In this commit, we carry out a new notion introduced during a recent
spec meeting to use a feature bit plus 100 before the feature has been
finalized in the spec.

We split into the Final and Staging bits.

feature/default_sets.go

@@ -83,7 +83,7 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
-	lnwire.SimpleTaprootChannelsOptional: {
+	lnwire.SimpleTaprootChannelsOptionalStaging: {
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},