Route: Attach blocks

- On admin report page, notify if region/block defined in route is not valid.

```yml
# file: my_module/config/routes.yml
routes:
  featured-products:
    template_string: "{{ 'featured_products'|drupalView }}"
    blocks:
      sidebar_second:
        - 'my_module:product_related'
        - ['my_module:product_ads', {title: "Ads"}]
```