feat: Set default GCP Scope (#16)

* feat: Set default GCP Scope

Update the GCP credential configuration to include a default scope for GCP access. The default scope is set to `https://www.googleapis.com/auth/cloud-platform` as recommended by [GCP's Best Practice](https://cloud.google.com/compute/docs/access/service-accounts#scopes_best_practice). This allows controlling the service account's access by granting it IAM roles.

plugin/service/host/README.md

@@ -26,7 +26,7 @@ boundary host-sets create plugin \
  -host-catalog-id HOST_CATALOG_ID \
  -name "Example Plugin-Based Host Set" \
  -description "Description for plugin-based host set" \
- -attr filters=status=RUNNING
+ -attr filters=status=RUNNING \
  -attr filters=labels.env:prod
 ```