HEEDLS-562 Add cancel back link to register admin first page

[AlexJacksonDS]

JIRA link

https://softwiretech.atlassian.net/browse/HEEDLS-562

Description

Added a missing cancel back link in the register admin journey.

Screenshots

---

Developer checks

I have:

• Run the formatter and made sure there are no IDE errors.
• Written tests for the changes (controller, data services, services, view models etc) and manually tested my work with and without JavaScript. Full manual testing guidelines can be found here: https://softwiretech.atlassian.net/wiki/spaces/HEE/pages/6703648740/Testing
• Updated/added documentation in Swiki and/or Readme.
• Updated my Jira ticket with information about other parts of the system that were touched as part of the MR and have to be sanity tested to ensure nothing’s broken.
• Scanned over my own MR to ensure everything is as expected.