Make CloudFormation tests optional and skip CFN finalizations when PR is unrelated to CloudFormation changes

[cmfcruz]

Running CloudFormation tests for PR unrelated to CloudFormation may block PR merges if the infrastructure has drifted and causes a CloudFormation test to fail. My suggestion is to make the CloudFormation tests optional if none of the changed files are related to CloudFormation. Likewise, finalization should skip CloudFormation actions if the merged PR has nothing to do with CloudFormation.

Aside from saving compute cycles, skipping CloudFormation tests or finalizations may avoid unexpected infrastructure changes caused by drifts. Rectification of drifts can cause outages as resources are modified or restarted.