Add external_ports to job automatically when prom_metrics_enabled

[busma13]

For Prometheus to collect metrics from a pod the port must be exposed using the external_ports field. https://terascope.github.io/teraslice/docs/configuration/clustering-k8s#external-ports

If prom metrics are enabled (either on the job or in terafoundation) the external ports field should automatically be added or modified in the jobConfig to expose the prom_metrics_port.