Adds openapi spec for POST /api/v2/spans including the json format

[codefromthecrypt]

See openzipkin/zipkin#1499 for the description of this format

I tested this with a deviation of @devinsba example here: openzipkin/zipkin-api-example#1

package main

import (
	"fmt"
	"log"
	"math/rand"
	"strconv"
	"time"

	httptransport "github.com/go-openapi/runtime/client"
	"github.com/go-openapi/strfmt"
	"github.com/openzipkin/zipkin-api-example/go/client"
	"github.com/openzipkin/zipkin-api-example/go/client/operations"
	"github.com/openzipkin/zipkin-api-example/go/models"
)

func main() {
	transport := httptransport.New("localhost:9411", "/api/v2", []string{"http"})
	zipkin := client.New(transport, strfmt.Default)

	id := uint64(rand.New(rand.NewSource(time.Now().UnixNano())).Int63())
	spanID := strconv.FormatUint(id, 16)
	timestamp := int64(time.Now().UnixNano() / int64(time.Microsecond))
	span := &models.Span{
		TraceID:   spanID,
		ID:        spanID,
		Kind:      models.SpanKindSERVER,
		Name:      "test",
		Timestamp: timestamp,
		Duration:  int64(200000),
		LocalEndpoint: &models.Endpoint{
			ServiceName: "testService",
			IPV4:        "192.228.233.62",
			Port:        80,
		},
		RemoteEndpoint: &models.Endpoint{
			IPV4: "192.228.233.62",
		},
		Tags: map[string]string{
			"http.path": "/api",
		},
	}

	resp, err := zipkin.Operations.PostSpans(
		operations.NewPostSpansParams().WithSpans(models.ListOfSpans{span}),
	)

	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(resp.Error()))
}

cc @kellabyte @basvanbeek

[codefromthecrypt]

PS for those curious, we don't have a read api for this model, yet. the zipkin2 project will take more time to complete, but POST endpoints are available now (in latest 1.30). POST is more important as that's what tracers use. The read apis will come, but later.

Follow openzipkin/zipkin#1644 for updates

[codefromthecrypt]

@flier @ellispritchard you might be interested in this, too

[codefromthecrypt]

PS I will add more detailed descriptions here as I noticed I had to link people to java files

[codefromthecrypt]

completed documentation

[codefromthecrypt]

updated validation script and switched current link to v2

[codefromthecrypt]

completed documentation

[ellispritchard]

Ta @adriancole !

[codefromthecrypt]

@pavolloffay fyi I know you are working on json and v1 couldn't be code-genned. You may still prefer to not codegen v2, but anyway here's the model for it.

[pavolloffay]

@adriancole thanks for pointing to this.