[Refactor] use constant variable for port name and value

[machichima]

• Convert hard-coded port names and values into constant variables defined in ray-operator/controllers/ray/utils/constant.go

kuberay/ray-operator/controllers/ray/utils/constant.go

Lines 66 to 77 in 732a675

	DefaultClientPort = 10001
	DefaultGcsServerPort = 6379
	DefaultDashboardPort = 8265
	DefaultMetricsPort = 8080
	DefaultDashboardAgentListenPort = 52365
	DefaultServingPort = 8000
	ClientPortName = "client"
	GcsServerPortName = "gcs-server"
	DashboardPortName = "dashboard"
	MetricsPortName = "metrics"
	ServingPortName = "serve"

Why are these changes needed?

Follow up on #3262 (comment)

Some codes include hard-coded port name and value, which may cause some typo.

Related issue number

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