Added new buttons methods

Features

• Added sendInteractiveButtons method
• Added sendInteractiveButtonsAsync method
• Added sendInteractiveButtonsReply method
• Added sendInteractiveButtonsReplyAsync method

Enhancements

• Updated docs for new methods
• Updated examples for new methods

Example:

greenAPI.sending.sendInteractiveButtons(
    "79001234567@c.us",
    "This is message with buttons!",
    [{
        "type": "call",
        "buttonId": "1",
        "buttonText": "Call me",
        "phoneNumber": "79001234567"
    },
    {
        "type": "url",
        "buttonId": "2",
        "buttonText": "Green-api",
        "url": "https://green-api.com/en/docs/api/sending/SendInteractiveButtons/"
    }],
    This is header",
    "This is footer"
)