Hey Liam!
I wrote another article about my whole process of deploying Gatsby to Netlify and Strapi to Heroku. The article includes a section where I described how to implement lifecycle hooks for the Strapi models under the models folder. Here is the article I wrote https://medium.com/javascript-in-plain-english/i-built-my-personal-website-using-gatsby-strapi-heroku-netlify-and-github-actions-879ca9098dab. Just scroll down to the header "Customized Webhooks To Trigger Repository Dispatch". That is the section where I go over how I wrote custom webhooks for Strapi to trigger the repository dispatch event. Let me know if my description there is lacking I can go over it and add more comments here!
Thanks,
Sanjar