DDLS-371: Show primary email in admin for client assigned to non primary

[Gugandeep]

Purpose

When an admin user views the details of a client, it also shows the details for the user account associated with that client.
This change will now show the primary user account details if the original associated user account was a non-primary account.

Fixes DDLS-371

Approach

• Change to frontend to check if the user associated with client is a primary account
• Call to new API endpoint to retrieve the primary account for a deputy uid
• Updated transformer and dto in API to bring back deputy_uid and is_primary
• Added api unit test
• Added behat test

Learning

Any tips and tricks, blog posts or tools which helped you. Plus anything notable you've discovered about DigiDeps

Checklist

• I have performed a self-review of my own code
• I have updated documentation (Confluence/ADR/tech debt doc) where relevant
• I have added tests to prove my work
• The product team have approved these changes
• I have checked my work for potential security issues and refered to the OWASP top 10

Frontend

• I have run an in-browser accessibility test (e.g. WAVE, Lighthouse)
• There are no deprecated CSS classes noted in the profiler
• Translations are used and the profiler doesn't identify any missing
• Any links or buttons added are screen reader friendly and contextually complete
• If adding GA events, I have updated or checked the existing category or label values

[Raffers]

As this is an admin action do we not want to limit this endpoint using a @security tag?