Introduce ProductFilterInterface::getChannel to allow further extension

[adrienlucas]

Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Fixed issue	N.A.

Following the introduction of \Synolia\SyliusAkeneoPlugin\Filter\ProductFilterInterface, I replaced the dependency between the ProductFiltersRules repository and the two CreateSimpleProductEntitiesTask and CreateConfigurableProductEntitiesTask by a dependency on ProductFilterInterface. In my case, it allows to reuse those tasks without having to fake the repository.

NB : I was tempted to move the initialization of $this->scope in the constructor of the tasks.. let me know if you find it a good idea !

[adrienlucas]

Not sure why the Behat tests are failing...