New Terraform Provider

To scaffold a new Terraform provider with Plugin Framework:

1. If I am already in a Terraform provider workspace, then confirm that I want
   to create a new workspace. If I do not want to create a new workspace, then
   skip all remaining steps.
1. Create a new workspace root directory. The root directory name should be
   prefixed with "terraform-provider-". Perform all subsequent steps in this
   new workspace.
1. Initialize a new Go module.
1. Run `go get -u github.com/hashicorp/terraform-plugin-framework@latest`.
1. Write a main.go file that follows [the example](assets/main.go).
1. Write an `internal/provider/provider.go` file that follows
   [the example](assets/provider.go). Rename the `demo` provider, the
   `DEMO_*` environment variables, and the authentication attributes to
   match the target API.
1. Remove TODO comments from `main.go` and `provider.go`.
1. Run `go mod tidy`
1. Run `go build -o /dev/null`
1. Run `go test ./...`
The scaffold resolves credentials as explicit config with environment
variable fallback. To grow that into a full credential provider chain
(shared credentials files, profiles, platform identity, configure-time
validation), use the `provider-configuration` skill (if available). To add
the first resource or data source, use the `provider-resources` skill (if
available).