Add the concept of conformance tests to roadmap

I believe this will be more and more valuable as others integrate with Kubecost.

ROADMAP.md

@@ -3,6 +3,7 @@ The following items are outstanding for the open source cost-model:
 __2022 roadmap__
 
 * Improved testing frameworks for backend APIs as well as frontend UI
+* Add conformance tests to confirm implementation meets standards
 * Deeper billing integrations with other cloud providers
 * More accessible & improved user interface
 * Improved support from open source community helm chart