Make it easier to 'tag' a Repo to a ContentType

[gggeek]

At the moment, when a Wrapper Repo is defined as a service, its definition often looks like this:

    my_site.repository.footer_link:
        class: My\SiteBundle\Repository\FooterLink
        parent: ezobject_wrapper.repository.abstract
        arguments:
            - '@ezpublish.api.repository'
            - '@ezobject_wrapper.entity_manager'
            - []
            - 'footer_link'
            - '@router'
        tags:
            -  { name: ezobject_wrapper.repository, content_type: footer_link }

We need to specify the footer_link ContentType twice:

• once (jn the tag) for the EntityManager to appropriately be able to associate it with the CT
• once (as argument for the constructor) for the case that the Repo is used as a service, ie. injected somewhere without going through the EM

As we don't want to make the latter usage unsupported, could we find a smarter way for the EM to be able to associate the service to the CT without having to specify it again?