Bad request because of bad URL encoding for dates

[thpiron]

Hello,

The dates used in query params don't use the webex API format: ISO8601.
So the server returns a 400 BAD REQUEST with the message: "The request could not be understood by the server due to malformed syntax.".

To reproduce:

package main

import (
	"fmt"
	"log"
	"time"

	webexteams "github.com/jbogarin/go-cisco-webex-teams/sdk"
)

// Client is Webex Teams API client
var Client *webexteams.Client

func main() {
	Client = webexteams.NewClient()

	myRoomID := "<yourRoomID>"

	messageQueryParams := &webexteams.ListMessagesQueryParams{
		RoomID: myRoomID,
		Before: time.Date(2022, time.August, 15, 0, 22, 12, 0, time.UTC),
	}

	messages, resp, err := Client.Messages.ListMessages(messageQueryParams)
	if err != nil {
		log.Fatal(err)
	}
	if resp.IsError() {
		log.Fatal(string(resp.Body()))
	}
	for id, message := range messages.Items {
		fmt.Println("GET:", id, message.ID, message.Text, message.Created)
	}
}

This PR fixes the issue: #27