Add support for global admin extensions via config

[core23]

Subject

Is is now possible to register a global admin extension via the configuration. This was only possible for tags.

The next step (new PR) is to allow all extension configuration for tags.

I am targeting this branch, because this feature is BC.

Changelog

### Added
- Add support for global admin extensions via config

[VincentLanglet]

There is

admins:
    specify one or more admin service ids to which the Extension should be added
excludes:
    specify one or more admin service ids to which the Extension should not be added (this will prevent it matching
    any of the other settings)
extends:
    specify one or more classes. If the managed class of an admin extends one of the specified classes the extension
    will be added to that admin.
implements:
    specify one or more interfaces. If the managed class of an admin implements one of the specified interfaces the
    extension will be added to that admin.
instanceof:
    specify one or more classes. If the managed class of an admin extends one of the specified classes or is an instance
    of that class the extension will be added to that admin.
uses:
    Specify one or more traits. If the managed class of an admin uses one of the specified traits the extension will be
    added to that admin.
priority:
    Can be a positive or negative integer. The higher the priority, the earlier it’s executed.

You should add a description of your new option too.

[core23]

This config was wrong for many years. If you do not have any extension, you should not register any invalid extension config.

E.g. the 'admins' => [] node tries to register something like this:

        sonata_admin:
            extensions:
                admins: []

The correct config should be something like this:

        sonata_admin:
            extensions:
                app.publish.extension:
                    global: true
                    admins:
                        - app.admin.article
                    implements:
                        - App\Publish\PublishStatusInterface
                    excludes:
                        - app.admin.blog
                        - app.admin.news
                    extends:
                        - App\Document\Blog
                    instanceof:
                        -  App\Document\Page
                    uses:
                        -  App\Trait\Timestampable

[VincentLanglet]

Now I understand what's doing this global options, do we need it ?

It can be done with

implements:
    - Sonata\AdminBundle\Admin\AdminInterface

isn't it ?

[VincentLanglet]

Ok, if I understand, this option already exists but was not usable in the config.
It makes sens to merge this, or deprecate the ability to do it for tags

[core23]

Now I understand what's doing this global options, do we need it ?

It can be done with

implements:
    - Sonata\AdminBundle\Admin\AdminInterface

isn't it ?

No implements is for model classes only, not for admin classes.

Ok, if I understand, this option already exists but was not usable in the config.
It makes sens to merge this, or deprecate the ability to do it for tags

My idea is to allow all options for the config and and tags.

[OskarStark]

Thanks @core23 😍