Add ability to setup Billing Alerts from Terraform

[loganmarchione]

Is your feature request related to a problem? Please describe.

The AWS Terraform provider has a resource called aws_budgets_budget that allows you to setup a budget (e.g., $5/month) and get a notification (e.g., email) when your usage goes over that amount.

https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/budgets_budget

Describe the solution you'd like

DigitalOcean has this feature, but it's not configurable via Terraform. I'm requesting it be added to the provider.

Describe alternatives you've considered

I don't see an API endpoint for this feature (where can I make a feature request?), but I'm guessing you could use this and grab the latest invoice and the amount?

https://docs.digitalocean.com/reference/api/api-reference/#operation/invoices_list

Additional context

N/A