Discuss new design for billing alerts in factories

[ludoo]

Following up on #1628 where @gustavovalverde raised the issue of billing alerts missing from the new project factory.

We recently created a new billing account module and moved billing alerts functionality inside it, so we are now ready to look at how to reimplement that functionality in factories.

My preference would be to add billing alert factory support to the billing account module, so alerts can be specified via a dedicated set of yaml files, and then either referencing existing alerts from the project factory, or combining it so the project data source can feed and populate the billling alerts data source.

[ludoo]

A billing alert factory was added to the billing module a few days ago. We are planning an overhaul of factories across the whole repo, closing this for now since billing is done.