channeldb: save resolver outcomes in close summaries top level bucket

Add a new top level bucket which holds closed channels nested by chain
hash which contains additional information about channel closes. We add
resolver resolutions under their own key so that we can extend the
bucket with additional information if required.

channeldb/db.go

@@ -157,6 +157,12 @@ var (
 			number:    16,
 			migration: migration16.MigrateSequenceIndex,
 		},
+		{
+			// Create a top level bucket which will store extra
+			// information about channel closes.
+			number:    17,
+			migration: mig.CreateTLB(closeSummaryBucket),
+		},
 	}
 
 	// Big endian is the preferred byte order, due to cursor scans over
@@ -277,6 +283,7 @@ var topLevelBuckets = [][]byte{
 	edgeIndexBucket,
 	graphMetaBucket,
 	metaBucket,
+	closeSummaryBucket,
 }
 
 // Wipe completely deletes all saved state within all used buckets within the