[FrameworkBundle] config:dump-reference command can now dump current configuration

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | I guess
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

I did not add `xml` support as I don't know how to do that. ping @stof 

sample:

```yaml
framework:
    secret: ThisTokenIsNotSoSecretChangeIt
    router:
        resource: /home/greg/dev/labs/se/app/config/routing_dev.yml
        strict_requirements: true
        http_port: 80
        https_port: 443
    form:
        enabled: true
        csrf_protection: { enabled: null, field_name: null }
    csrf_protection:
        enabled: true
        field_name: _token
    validation:
        enable_annotations: true
        enabled: true
        translation_domain: validators
    templating:
        engines: [twig]
        assets_version: null
        assets_version_format: '%%s?%%s'
        hinclude_default_template: null
        form: { resources: ['FrameworkBundle:Form'] }
        assets_base_urls: { http: {  }, ssl: {  } }
        loaders: {  }
        packages: {  }
    default_locale: en
    trusted_hosts: {  }
    trusted_proxies: {  }
    session:
        storage_id: session.storage.native
        handler_id: session.handler.native_file
        save_path: /home/greg/dev/labs/se/app/cache/dev/sessions
        metadata_update_threshold: '0'
    fragments:
        enabled: true
        path: /_fragment
    http_method_override: true
    profiler:
        only_exceptions: false
        enabled: true
        collect: true
        only_master_requests: false
        dsn: 'file:/home/greg/dev/labs/se/app/cache/dev/profiler'
        username: ''
        password: ''
        lifetime: 86400
    ide: null
    esi:
        enabled: false
    translator:
        enabled: false
        fallback: en
    annotations:
        cache: file
        file_cache_dir: /home/greg/dev/labs/se/app/cache/dev/annotations
        debug: true
    serializer:
        enabled: false
```