add docs.rs domain to fastly

[marcoieni]

The same is present in

simpleinfra/terragrunt/modules/crates-io/fastly-static.tf

Line 33 in b7764c9

domain {

[marcoieni]

got the error

╷
│ Error: 400 - Bad Request:
│
│     Title:  Can't update subscription
│     Detail: Subscription has active domains
│
│   with module.fastly_tls_subscription_globalsign.fastly_tls_subscription.subscription,
│   on ../fastly-tls-subscription/main.tf line 1, in resource "fastly_tls_subscription" "subscription":
│    1: resource "fastly_tls_subscription" "subscription" {
│
╵

[marcoieni]

applied by reducing the scope of the PR