Add required selector to VPA deployment examples for apps/v1

[kcmartin]

The VPA example deployments were recently switched to apps/v1. [#2209 ]

While attempting kubectl create -f examples/hamster.yaml the following error was revealed:

error: error validating "examples/hamster.yaml": error validating data: ValidationError(Deployment.spec): missing required field "selector" in io.k8s.api.apps.v1.DeploymentSpec

I found this was due to apps/v1 requiring that .spec.selector and .metadata.labels be explicitly set:
https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#selector

This PR updates the examples to conform to apps/v1

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[jbartosik]

/lgtm
/approve

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