Add license management capability to coderd provider

[johnstcn]

Should allow adding / removing licenses, e.g.:

resource "coderd_license" "license" {
  license = kubernetes_secret.license.data["license.json"]
}

[ethanndickson]

Terraform doesn't provide us, as provider developers, with a way to require that a specific resource type be created before others. This makes the UX of a license resource kind of awkward - you'd have to apply it before the rest of your config, if any part of that config wants to use enterprise/premium features.

One nicer way to implement it would be making it an optional attribute on the provider itself. I suspect this is what we'll end up going with.

EDIT: I changed my mind on this - Terraform has the depends_on meta-argument for a reason, whilst you might run into trouble if you forget to include it, needing to use depends_on shouldn't be surprising for anyone familiar with Terraform.