AZURE_PRIVATE_DNS: Enable automated testing

[TomOnTime]

Issue

Automated testing of AZURE_PRIVATE_DNS was not set up.

Resolution

1. The AZURE_PRIVATE_DNS variables were not set. Create them in the Azure portal and set them in the GHA secrets.
2. Update profiles.json with the variable names.
3. Document the lazy way to create credentials.

[TomOnTime]

CC @matthewmgamble