graph/db: make some ChannelEdgeInfo fields optional

Since not all will be required for V2 channels.

Wrap BitcoinKey1Bytes and BitcoinKey2Bytes in fn.Option since these
fields are only required for v1 channel announcements. V2 channels may
or may not have bitcoin keys present in their announcement.

NewV1Channel constructor wraps the bitcoin keys with fn.Some().
All access sites updated to unwrap the options, using UnwrapOr for
non-critical paths and UnwrapOrErr where the keys must be present
(e.g., KV serialization, ToChannelAnnouncement).

graph/db/sql_store.go

@@ -4288,15 +4288,19 @@ func insertChannel(ctx context.Context, db SQLQueries,
 	}
 
 	createParams := sqlc.CreateChannelParams{
-		Version:     int16(v),
-		Scid:        channelIDToBytes(edge.ChannelID),
-		NodeID1:     node1DBID,
-		NodeID2:     node2DBID,
-		Outpoint:    edge.ChannelPoint.String(),
-		Capacity:    capacity,
-		BitcoinKey1: edge.BitcoinKey1Bytes[:],
-		BitcoinKey2: edge.BitcoinKey2Bytes[:],
+		Version:  int16(v),
+		Scid:     channelIDToBytes(edge.ChannelID),
+		NodeID1:  node1DBID,
+		NodeID2:  node2DBID,
+		Outpoint: edge.ChannelPoint.String(),
+		Capacity: capacity,
 	}
+	edge.BitcoinKey1Bytes.WhenSome(func(vertex route.Vertex) {
+		createParams.BitcoinKey1 = vertex[:]
+	})
+	edge.BitcoinKey2Bytes.WhenSome(func(vertex route.Vertex) {
+		createParams.BitcoinKey2 = vertex[:]
+	})
 
 	if edge.AuthProof != nil {
 		proof := edge.AuthProof