Added validation for YAML keys

````
| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes - if the user had invalid configuration and that worked for them
| Deprecations? | no
| Tests pass?   | 
| Fixed tickets | https://github.com/symfony-cmf/RoutingAutoBundle/issues/123
| License       | MIT
| Doc PR        |
````