Add order_comments

This PR will add order_comments (customer’s comment) to message template:

file Classes/WooCommerce.php

public function filterTemplate($replace){
        $replace['{order_id}'] = $this->order_id;
        $replace['{order_comments}'] = $this->order->get_customer_note();
        $replace['{order_status}'] = wc_get_order_status_name($this->order->get_status());
        $replace['{total}'] = wc_price($this->order->get_total());
        $replace['{order_date_created}'] = $this->order->get_date_created()->date(get_option('links_updated_date_format'));
        return $replace;
    }

file Classes/SettingPage.php

<div class="row">
            <table class="form-table">
                <tbody>
                <tr>
                    <th></th>
                    <td> <button id="nktgnfw_send_test_message" type="button" class="button-primary"><?= __('Send test message','nktgnfw')?></button></td>
                </tr>
                <tr>
                    <th><h4><?= __('Allow tags for Telegram Message', 'nktgnfw') ?></h4></th>
                    <td><textarea class="code wp-editor-area" rows="15" readonly><b>bold</b>
<strong>bold</strong>
<i>italic</i>
<em>italic</em>
<u>underline</u>
<ins>underline</ins>
<s>strikethrough</s>
<strike>strikethrough</strike>
<del>strikethrough</del>
<a href="https://www.domain.com/">inline URL</a>
<code>code</code>
<pre>code block</pre></textarea></td>
                </tr>
                <tr>
                    <th><h4><?= __('Shortcodes for Telegram Message', 'nktgnfw') ?></h4></th>
                    <td><textarea class="code wp-editor-area" rows="15" readonly>{order_comments}
{order_id}
{order_date_created}
{order_status}
{products}
{total}
{billing-first_name}
{billing-last_name}
{billing-address_1}
{billing-address_2}
{billing-city}
{billing-state}
{billing-postcode}
{billing-email}
{billing-phone}
{payment_method}
{payment_method_title}
{customer_ip_address}
{customer_user_agent}
                        </textarea></td>
                </tr>
                <tr>
                    <th></th>
                    <td><?= wp_kses(__("Visit <a href='https://choplugins.com' target='_blank'>our website</a> to get more useful plugins", "nktgnfw"), ['a' => ['href' => 'https://choplugins.com','target' =>'_blank']]); ?></td>
                </tr>
                </tbody>
            </table>
        </div>