Add ability to specify dnsConfig in helm chart (#1344 )

* Update values.yaml

* Update deployment.yaml

* Update charts/metrics-server/templates/deployment.yaml

Co-authored-by: Steve Hipwell <steve.hipwell@gmail.com>

* Update helm chart README to add dnsConfig

* Fix curly braces as default input for dnsConfig

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Co-authored-by: Steve Hipwell <steve.hipwell@gmail.com>

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