Email-rendering: configure template unsubscribe links etc

## Issue

We have [endpoints in email](https://github.com/guardian/email-rendering/blob/main/src/notificationApp/index.ts) rendering for generating notification emails from requests sent by the notifications tool

They are as expected visually, but we need to ensure that they are functional for production IE:
- in-content links point to the right pages and are correctly attributed to the user with they tracking tokens
- the unsubscribe links in the footer work
- the legal text at the bottom of the email is accurate

## Solution
Check how the email output is generated in email rendering and modified by the Braze campaign template using the recipient data. May require:
- changing the notification email template in email rendering
- providing extra parameters from the notifications tool backend
- adding parameters to the Braze campaign template.