Add StatusCake for the test environment

[vacabor]

Enables the StatusCake module and uses the existing contact groups for alerting.

[AbigailMcP]

Do we need to set the external_url variable in test.tfvars.json to be our healthcheck url?

[vacabor]

Do we need to set the external_url variable in test.tfvars.json to be our healthcheck url?

statuscake.tf takes care of setting a check on the healthcheck URL by getting it from the application module, but I've also set external_url so we can have an extra SSL check on /additional-payments/claim

[vacabor]

Do we need to set the external_url variable in test.tfvars.json to be our healthcheck url?

statuscake.tf takes care of setting a check on the healthcheck URL by getting it from the application module, but I've also set external_url so we can have an extra SSL check on /additional-payments/claim

I've reverted this - it's something we can set on production, but for test the endpoint is protected by HTTP basic (so the StatusCake check always fails).