Add composite ConfigStore to combine multiple ConfigStore (#3027)

In some repositories, we used multiple ConfigStores to store feature
flags, for example, in eventing kafka broker, we use the Eventing
core feature flags store and the EKB feature flags store

Signed-off-by: Pierangelo Di Pilato <pierdipi@redhat.com>

reconciler/configstore.go

@@ -20,6 +20,20 @@ import "context"
 
 // ConfigStore is used to attach the frozen configuration to the context.
 type ConfigStore interface {
-	// ConfigStore is used to attach the frozen configuration to the context.
+	// ToContext is used to attach the frozen configuration to the context.
 	ToContext(ctx context.Context) context.Context
 }
+
+// ConfigStores is used to combine multiple ConfigStore and attach multiple frozen configurations
+// to the context.
+type ConfigStores []ConfigStore
+
+// ConfigStores implements ConfigStore interface.
+var _ ConfigStore = ConfigStores{}
+
+func (stores ConfigStores) ToContext(ctx context.Context) context.Context {
+	for _, s := range stores {
+		ctx = s.ToContext(ctx)
+	}
+	return ctx
+}