Instead of adding a new .html.erb template file I updated the existing user’s invite template to include topic/PM link (similar to what we do for new user invite link) in topic title and at the bottom of email. This also allows staff to use and repurpose topic_link as they see fit while customizing invite email template.
https://github.com/discourse/discourse/commit/600233482f3bf499e7655a1596908eee32f8cbbb
Topic:
PM:
