Manage the agent API service account and token in Terraform

The Authentik API token used by estate automation was created by hand in the
UI and pasted into Vault, so it was undocumented, unauditable and impossible
to rotate reproducibly. Model it as config instead.

Add a service_accounts config kind, discovered from config/service_accounts/
like the other kinds. Each entry creates a service_account user, an RBAC role
carrying its global permissions, its API tokens, and (optionally) a kv-v2
write publishing each token key.

Add sa-agent-api granting view_outpost, view_token and view_token_key, with a
non-expiring api token agent-api-token published to kv/service/authentik/agent-api-token.

environments/identity.k8s.syd1.au.unkin.net/terragrunt.hcl

@@ -23,4 +23,5 @@ inputs = {
   providers_saml    = local.config.providers_saml
   providers_oauth2  = local.config.providers_oauth2
   providers_ldap    = local.config.providers_ldap
+  service_accounts  = local.config.service_accounts
 }