Add verify-cloudformation script

[rifelpet]

This is an official AWS linter for cloudformation: https://github.com/aws-cloudformation/cfn-python-lint

It has already caught a few bugs in our cloudformation json generation logic. Examples:

E3002 Invalid Property Resources/AWSAutoScalingAutoScalingGroupnodesmixedinstancesexamplecom/Properties/MixedInstancesPolicy/InstancesDistribution/SpotInstancePool
//kops/tests/integration/update_cluster/mixed_instances_spot/cloudformation.json:321:13

E3031 CidrIp contains invalid characters (Pattern: x.x.x.x/y) at Resources/AWSEC2SecurityGroupIngresssshexternaltonode2001085a348/Properties/CidrIp
//kops/tests/integration/update_cluster/complex/cloudformation.json:833:9

I3011 The default action when replacing/removing a resource is to delete it. Set explicit values for UpdateReplacePolicy / DeletionPolicy on potentially stateful resource: Resources/AWSEC2Volumeustest1aetcdeventsprivateciliumexamplecom
//kops/tests/integration/update_cluster/privatecilium2/cloudformation.json:1227:5

It currently exits 0 while we add it to the presubmit jobs. Once we address the issues we'll update it to exit nonzero if there are regressions.

ref: #10015

[k8s-ci-robot]

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[rifelpet]

/test pull-kops-bazel-test

[hakman]

/lgtm

[hakman]

/retest