Add support for virtual file system storages

[optik-aper]

Description

This adds support for managing VFS storages.

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran tests with your changes locally?

Testing instructions

You can emulate these test funcs to check each route available through the govultr library:

func vfsList(ctx context.Context, client *govultr.Client) {
	vfss, _, _, err := client.VirtualFileSystemStorage.List(ctx, nil)
	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", vfss)
}

func vfsGet(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	vfs, _, err := client.VirtualFileSystemStorage.Get(ctx, id)
	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", vfs)
}

func vfsCreate(ctx context.Context, client *govultr.Client) {
	vfs, _, err := client.VirtualFileSystemStorage.Create(ctx, &govultr.VirtualFileSystemStorageReq{
		Region: "ewr",
		Label:  "govultr-test",
		StorageSize: govultr.VirtualFileSystemStorageSize{
			SizeGB: 10,
		},
		DiskType: "nvme",
		Tags: []string{
			"test-vfs",
			"delete-after-testing",
		},
	})

	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", vfs)
}

func vfsUpdate(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	vfs, _, err := client.VirtualFileSystemStorage.Update(ctx, id, &govultr.VirtualFileSystemStorageUpdateReq{
		Label: "govultr-test-upd",
		StorageSize: govultr.VirtualFileSystemStorageSize{
			SizeGB: 20,
		},
	})

	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", vfs)
}

func vfsDelete(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	if err := client.VirtualFileSystemStorage.Delete(ctx, id); err != nil {
		fmt.Println(err)
		panic(err.Error())
	}
}

func vfsAttach(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	targetID := "4f05ab05-a560-4bce-8158-7088aaf5de78"
	att, _, err := client.VirtualFileSystemStorage.Attach(ctx, id, targetID)
	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", att)
}

func vfsAttachmentList(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	atts, _, err := client.VirtualFileSystemStorage.AttachmentList(ctx, id)
	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", atts)
}

func vfsAttachmentGet(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	targetID := "4f05ab05-a560-4bce-8158-7088aaf5de78"
	att, _, err := client.VirtualFileSystemStorage.AttachmentGet(ctx, id, targetID)
	if err != nil {
		fmt.Println(err)
		panic(err.Error())
	}

	fmt.Printf("%+v", att)
}

func vfsDetach(ctx context.Context, client *govultr.Client) {
	id := "0ae69c69-0c46-4ab3-8601-c86a39b1026e"
	targetID := "4f05ab05-a560-4bce-8158-7088aaf5de78"
	if err := client.VirtualFileSystemStorage.Detach(ctx, id, targetID); err != nil {
		fmt.Println(err)
		panic(err.Error())
	}
}

[christhemorse]

Looks good!