Connect to the new HMRC API developer hub

HMRC are currently updating their dat connection service to a modern API service: see details here:

https://developer.service.hmrc.gov.uk/api-documentation/docs/using-the-hub

Note: Reckon UK has registered the product 'Reckon One UK' as an application. Let @Jon Martingale know if you need access to the application service.

The new API is not yet live and is unlikely to be when we launch the Payroll UK module. However, we need to consider the API in our plans to ensure we can switch.

Connecting to the API will also be relevant for VAT and VAT filing.