Bump vault-secrets-arrstack provider to 0.2.0 and plumb methods

Engine plugin v0.2.0 (catalog bumped in #144) added a methods field to
arrstack roles, pinning a minted arrproxy key to a set of HTTP methods.
Provider v0.2.0 exposes it as an optional set attribute, but the module
had no input for it, so no role yaml could use it.

- Bumps the vault-secrets-arrstack provider pin from 0.1.1 to 0.2.0 in
  root.hcl and both arrstack modules
- Adds an optional methods input to arrstack_secret_backend_role and
  passes it through to the resource
- Threads methods through the vault_cluster arrstack_secret_backend_role
  object type so a role yaml may carry a methods: list

methods defaults to null rather than [], matching the provider's null
read-back for an unrestricted role, so existing role yamls need no change
and plan stays a provider-version-only diff.

environments/root.hcl

@@ -67,7 +67,7 @@ terraform {
     }
     arrstack = {
       source  = "artifactapi.k8s.syd1.au.unkin.net/terraform-unkin/vault-secrets-arrstack"
-      version = "0.1.1"
+      version = "0.2.0"
     }
   }
 }