graph/db: split HasNode into two methods

HasNode currently is very v1 specific since it returns a time.Time
timestamp which is specific to V1 node announcements. However, it is
mostly only used for the "exists" return value. So here we split it up
into HasNode which just checks existence and HasV1Node which retains the
same behavaiour as before.

graph/db/interfaces.go

@@ -119,12 +119,19 @@ type Store interface { //nolint:interfacebloat
 	FetchNode(ctx context.Context, nodePub route.Vertex) (*models.Node,
 		error)
 
+	// HasV1Node determines if the graph has a vertex identified by
+	// the target node identity public key in the V1 graph. If the node
+	// exists in the database, a timestamp of when the data for the node
+	// was lasted updated is returned along with a true boolean. Otherwise,
+	// an empty time.Time is returned with a false boolean.
+	// This is specific to the V1 graph since only V1 node announcements
+	// use timestamps for their latest update timestamp.
+	HasV1Node(ctx context.Context, nodePub [33]byte) (time.Time, bool,
+		error)
+
 	// HasNode determines if the graph has a vertex identified by
-	// the target node identity public key. If the node exists in the
-	// database, a timestamp of when the data for the node was lasted
-	// updated is returned along with a true boolean. Otherwise, an empty
-	// time.Time is returned with a false boolean.
-	HasNode(ctx context.Context, nodePub [33]byte) (time.Time, bool, error)
+	// the target node identity public key.
+	HasNode(ctx context.Context, nodePub [33]byte) (bool, error)
 
 	// IsPublicNode is a helper method that determines whether the node with
 	// the given public key is seen as a public node in the graph from the