NGSTACK-442: implement internal Content view route config

[pspanja]

There a several problems with having Internal eZ Platform Content view route (_ez_content_view) on a frontend siteaccess:

• it generates the selected view using default templates from eZ Platform kernel
• it might present a security risk
  • it allows rendering of Content that might not be intended to be directly available (eg. various configuration objects)
  • it allows choosing a view and a Location
• it does not redirect to the URL alias route

This implementes rendering of the route through Site API and a configuration to control whether the route will be active on a frontend siteaccess and how it will behave (showing defaults):

ezpublish:
    system:
        frontend_group:
            ng_site_api:
                enable_internal_view_route: true
                redirect_internal_view_route_to_url_alias: true

The route will be enabled by default and will permanently redirect to the URL alias. If disabled, or if the URL alias can't be generated, 404 will be thrown. If enabled without redirect, it will render the Content through the Site API, instead of using default eZ templates.

[pspanja]

Updated as discussed in private; now the internal route is by default enabled, and will permanently redirect to the URL alias.

[pspanja]

Thanks @emodric