allow recipes to work with php config files (instead of default yaml) about symfony

[k0d3r1s]

this looks like flex thing: https://github.com/symfony/flex
biggest problem here is to copy right config from recipe, adding .php config to recipe seems already doable. adding both .yaml and .php now would copy both files to project

[stof]

We don't maintain 2 variants of each recipe to use either Yaml or PHP config files. So if you want to rely on the Flex recipes, you need to stick to Yaml for now.

[xabbuh]

let's close here in favor of symfony/flex#970

[arderyp]

Thanks for the confirmation and the link to the other issue :)