Add Snapshot Repository API

[Flygsand]

This PR adds support for Elasticsearch's snapshot repository API.

Example program:

package main

import (
	"context"
	"fmt"

	elastic "gopkg.in/olivere/elastic.v5"
)

type FSSettings struct {
	Location string `json:"location"`
}

func main() {
	client, err := elastic.NewClient()
	if err != nil {
		panic(err)
	}

	repo := new(elastic.SnapshotRepository)
	repo.Type = "fs"
	settings := new(FSSettings)
	settings.Location = "/tmp/elasticsearch"
	repo.Settings = settings

	_, err = client.SnapshotCreateRepository("repo1").BodyJson(repo).Do(context.TODO())
	if err != nil {
		panic(err)
	}

	repos, err := client.SnapshotGetRepository("repo1").Do(context.TODO())
	if err != nil {
		panic(err)
	}
	fmt.Printf("%v\n", repos)

	verify, err := client.SnapshotVerifyRepository("repo1").Do(context.TODO())
	if err != nil {
		panic(err)
	}
	fmt.Printf("%v\n", verify.Nodes)

	_, err = client.SnapshotDeleteRepository("repo1").Do(context.TODO())
	if err != nil {
		panic(err)
	}
}

[olivere]

Awesome. Thanks for sharing. Would definitely like to add this to elastic!

I build the services from the REST API specification. There's even a code generator in the generate-api branch. Did you use that to create the skeleton of the services?

[Flygsand]

That would explain why some of the code had a generation feel to it :). No, I was not aware of this workflow. Copy-pasted together most of it. Anyway, ran the generator and updated the PR.