fix dev-build following pan-domain-authentication changes

[twrichards]

What is the value of this and can you measure success?

dev-build has been broken since #27012 owing to a missing implementation - this is problematic for devs (in particular @guardian/dotcom-platform

What does this change?

Moves the instantiation of GuardianAuthWithExemptions which was introduced in #27012 up to the AdminControllers trait which is shared by the dev-build and the real AppComponents since they both need it.

Checklist

• Tested locally, and on CODE if necessary
• Will not break dotcom-rendering
• Will not break our database – if updating CAPI, updated and committed the database files
• Meets our accessibility standards
  • Tested with screen reader
  • Navigable with keyboard
  • Colour contrast passed

[github-actions]

Deploy build 1765 of dotcom:frontend-all to CODE

All deployment options

• Deploy build 1765 of dotcom:frontend-all to CODE
• Deploy parts of build 1765 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.

[prout-bot]

Seen on FRONTS-PROD, ADMIN-PROD (merged by @twrichards 13 minutes and 4 seconds ago)

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