cluster: introduce NodeID and ZoneID types

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/cluster/types.go

@@ -0,0 +1,25 @@
+package cluster
+
+import "strconv"
+
+type (
+	// ZoneID is the identifier of a [Zone]
+	ZoneID int
+	// NodeID is the identifier of a [Machine]
+	NodeID int
+)
+
+func (z ZoneID) String() string {
+	return idString(int(z))
+}
+
+func (n NodeID) String() string {
+	return idString(int(n))
+}
+
+func idString(v int) string {
+	if v > 0 {
+		return strconv.Itoa(v)
+	}
+	return ""
+}