[Idea] Support track_links for the text version of emails

[louis-antonopoulos]

I see that at the top of AhoyEmail::Processor#track_links, there is an explicit check for if html_part?.

I'd love to open a PR to add tracking to the text-only version of an email.

Is that something that you think would be beneficial to the community, or was there a product decision to only attempt to parse the html component of a mailer?

Thanks!

[louis-antonopoulos]

One challenge I see with attempting to add tracking to links in text-based emails would be how to accurately identify unsubscribe links with respect to the AhoyEmail.default_options[:unsubscribe_links] configuration setting.