Add support for numeric ports

[jtuchel]

• I have looked at the documentation here first?
• I have looked at the examples provided that may showcase my question here?

Package version eg. v9, v10:

v10

Issue, Question or Enhancement:

Please add support for numeric ports, e.g. a port of type uint. For now we have two options

• use hostname_port and pass in a string, e.g. ":8080"
• use a custom validation, e.g. validate:"gte=1,lte=65535"

Code sample, to showcase or reproduce:

The solution would be very similiar to this implementation

https://github.com/go-playground/validator/blob/master/baked_in.go#L2675

The keyword could be port, the implementation could be

func isPort(fl FieldLevel) bool {
	val := fl.Field().Uint()
	
	return val >= 1 && val <= 65535
}

[zandwang]

very good proposal, hope to merge as soon as possible