[CI] Unable to test only specific platform

Summary

Currently we can only execute pipeline across all the defined platforms: GKE-vX.{Y,Y-N}, EKS, etc. For efficiency purposes it would be great if we can execute only single platform at a time, for example - "only eks" thus freeing up resources and speeding up pipeline execution time.

Current behavior

Execute pipeline across all platforms

Expected behavior

Run for a single requested platform.

Implementation plan

• Compartmentalize each platform
• Add mechanism for conditional platform inclusion