Add openapi:generate Meta support to dsl.Server

[tchssk]

Usage

Server("test", func() {
	Host("localhost", func() {
		URI("https://goa.design")
	})
	Meta("openapi:generate", "false")
})

The suppressed documents

openapi.json

"host": "goa.design",

openapi.yaml

host: goa.design

openapi3.json

"servers": [
    {
        "url": "https://goa.design"
    }
],

openapi3.yaml

servers:
    - url: https://goa.design

[raphael]

This is great, thank you!