Proposal: x-omitempty for general types

[zhuangqh]

Problem statement

Currently, we use x-omitempty to exclude null array value. related PR #1189
Maybe x-omitempty can support general type to control the omityempty tag.

Foo:
  type: "object"
  properties:
    hasOmitEmptyTrue:
      type: string
      x-omitempty: true
    hasOmitEmptyFalse:
      type: string
      x-omitempty: false

produce

type Foo struct {
	// has omit empty false
	HasOmitEmptyFalse string `json:"hasOmitEmptyFalse"`
	// has omit empty true
	HasOmitEmptyTrue string `json:"hasOmitEmptyTrue,omitempty"`
}

Swagger specification

Steps to reproduce

Environment

swagger version: x.x.x
go version: x.x.x
OS:

[fredbi]

Closed with #1751