[Improvement] ["feature" request] Flex support

[kptLucek]

Hi there!

As within company we're updating our packages to work with symfony/flex and their recipes i've discovered, that at least few of our packages has this bundle required as dependency.

As configuring "vendors" by "vendors" is inconvenient as dependency may change during it's development (which also applies to it's configuration and requirements) it seems that i/we have two options:

Option A)
Suggest integrating this package with flex More here which would save potential duplication within packages that use this package as their dependency

Option B)
Oven if "our" packages get "upgraded" to work with flex, we have to still require "manual" stuff from developer using our package to manually copy/paste (in this case) yours configuration.

--
As creating configuration for flex is pretty quick and easy i know, that we all lack of time for, however i can prepare such for this package and open PR within Flex Contrib Repository in your behalf to speed migration process up.