Allow updating and configuring other than YAML configuration formats (XML, PHP, Attributes)

[kaznovac]

As a developer I would like to configure/update symfony app's configuration files with my choice of configuration file format.

symfony/flex should allow developer to state the format of the configuration files (or even try to detect them from the application at hand)

Lack of this feature greatly hinders usability of flex's recipes:update for non-yaml configurations

related: #791

[arderyp]

Agreed, this would be slick, especially given compelling reasons for using php configs over yaml, which is suspect will become the new norm

https://getrector.com/blog/modernize-symfony-configs