Add optional parameter ambassadorNodePort

[iankoulski]

Used to set the ambassador service nodePort only when ambassadorServiceType is NodePort and ambassadorNodePort is within the valid range [30000-32767]. By default this parameter is set to 0. If ambassadorServiceType is NodePort and ambassadorNodePort is outside the valid range, then Kubernetes will automatically assign an available nodePort.

Contributes to closing the following issues:
#630
#1525

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This change is 

[k8s-ci-robot]

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[kunmingg]

/lgtm
/approve

[k8s-ci-robot]

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[kunmingg]

/ok-to-test