✨ Add support for polls

[Log1x]

In preparation for discord-php/DiscordPHP#1226

Example usage:

$this
    ->message()
    ->poll('What is your favorite color?', [
        '🔴' => 'Red',
        '🟢' => 'Green',
        '🔵' => 'Blue'
    ], duration: 24, multiselect: true)
    ->reply($message);