[AdminUi] Add a Twig global variable for the context

[loic425]

Add a better DX for the admin ui context.

- {% set dashboard_path = hookable_metadata.context.routing.dashboard_path|default('/admin') %}
+ {% set dashboard_path = sylius_admin_ui_context.routing.dashboardPath %}

Then, we have an autocompletion on our IDE.

[diimpp]

Do you need both?

[loic425]

that's automatical now, after the composer install. Here, it's only on the test application.

[diimpp]

Should both Context and RoutingContext have interfaces? In case I would want to override those classes at end-user projects.

[loic425]

I don't want user to change those contexts for now. That's only to bring access to admin ui configuration.

[NoResponseMate]

Either interfaces or some other extension point would be great, but yeah, it could be added at a later date.

[loic425]

Yes but before adding some extension point, it's preferable to be stable on data accessors. I think I need to add login path and things like that before. Or just adding the interface on the main context class.

[loic425]

I really didn't think it through; we can use the routes provided now.
Replaced by #283