Allow customization of Customer Portal Approval screen

As a Jira Service Desk Administrator, I want to customize the Customer Portal approval process to include comments and other fields, so that I can reduce the reliance on email functionality internally.

Customize the Customer Portal in a fashion similar to the currently available email notifications customizations *(Managing service desk notifications, *Include issue variables).

Notes:

As of Jira Service Desk 4.4.1, the approval URL for the Customer Portal is

https://<instance>/servicedesk/customer/user/approval-action/.../24/approve

According to Atlassian documentation Approving a service desk request:

Pro tip: Ask your Project Administrator to add Request details and Approval buttons to your approval notifications template, so you can quickly action a request from within your email.

customers are currently able to edit the notifications template but not the Customer Portal pages, which increases internal reliance on email.