Sylius version affected: 1 and 2

Description
When using the default Grid Action, I must define a route even if I already defined a url. I should be able to not define a route, because the URL is already defined.

Steps to reproduce
Create a button in the grid with the "default" template, and only define the options.link.url .

sylius_grid:
    grids:
        sylius_admin_exchange_rate:
            actions:
                main:
                    custom_url:
                        type: default
                        label: test
                        options:
                            link:
                                url: '/my-custom-url'
                              # route: 'sylius_admin_exchange_rate_index' # needed to work right now

Possible Solution
It seems that the default function is still called even if route is already defined.
It should be able to add a check if URL is defined, then we don't need to have a default route.

{% set path = options.link.url|default('') is not empty ? options.link.url : path(options.link.route, options.link.parameters|default({})) %}

UPDATE :
I just saw the AdminBundle/templates/shared/grid/action/links.html.twig:19 file where the links are handled this way :

{% set path = link.url is defined ? link.url : path(link.route, link.parameters|default([])) %}