User-Agent string format

[kaittodesk]

Current User-Agent string does not follow common practices of User-Agent strings used by libraries and web browsers:

WordPress/5.5.1; https://example.com; WooCommerce/4.6.1; smaily-for-woocommerce/1.6.0

The common practice is to provide the plugin's name and version as the first item and rest of the metadata in parenthesis following the name and version. For example:

smaily-for-woocommerce/1.6.0 (WordPress/5.5.1; WooCommerce/4.6.1; +https://example.com)

I recommend we update the format of the User-Agent string in the plugin to latter example.