lnwallet: add new AuxFundingDesc struct

This struct will house all the information we'll need to do a class of custom channels that relies primarily on adding additional items to the tapscript root of the HTLC/commitment/funding outputs.

Author: Roasbeef

lnwallet/wallet.go

@@ -31,6 +31,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chanvalidate"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/shachain"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 const (
@@ -89,6 +90,33 @@ func (p *PsbtFundingRequired) Error() string {
 	return ErrPsbtFundingRequired.Error()
 }
 
+// AuxFundingDesc stores a series of attributes that may be used to modify the
+// way the channel funding occurs
+type AuxFundingDesc struct {
+	// CustomFundingBlob is a custom blob that'll be stored in the database
+	// within the OpenChannel struct. This should represent information
+	// static to the channel lifetime.
+	CustomFundingBlob tlv.Blob
+
+	// TapscriptRoot is the root of the tapscript tree that will be used to
+	// create the funding output.
+	TapscriptRoot chainhash.Hash
+
+	// CustomLocalCommitBlob is a custom blob that'll be stored in the
+	// first commitment entry for the local party.
+	CustomLocalCommitBlob tlv.Blob
+
+	// CustomRemoteCommitBlob is a custom blob that'll be stored in the
+	// first commitment entry for the remote party.
+	//
+	// TODO(roasbeef): have this just use the leaf fetcher?
+	CustomRemoteCommitBlob tlv.Blob
+
+	// InitAuxLeaves is the set of aux leaves that'll be used for the very
+	// first commitment state.
+	InitAuxLeaves CommitAuxLeaves
+}
+
 // InitFundingReserveMsg is the first message sent to initiate the workflow
 // required to open a payment channel with a remote peer. The initial required
 // parameters are configurable across channels. These parameters are to be