@James Bennett Thanks for posting your question in Microsoft Q&A, apologize for any inconvenience caused on this.
I understand that you are looking for minimum RBAC role to enable remote debugging on app service using 'az webapp config set' cmdlet.
If my understanding is correct, then you can create a customer role with this permission 'Microsoft.Web/sites/config/Write' so that particular user can update the configuration of the app service.
You can also refer to this documentation for more permissions available at resource provider level.
Hope this help! Let me know if you have any further questions on this.