Make parsers configurable

[Aeliot-Tm]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	yes
Documented?	yes
License	MIT

Add possibility to configure parsers.
This is necessary for supporting of Apollo Federation Entities.

[Vincz]

Hi @Aeliot-Tm!
Parsing is something have been working on a few months back.
The idea was to handle it as proper Symfony services allowing to extend it using all the tools Symfony has to offer.
Unfortunately , I have been able to find the time to work on it but it was almost finished.
You can check the latest version here : https://github.com/vincz/GraphQLBundle
The various parsers were exploded into different packages (including under configuration/ in the repository).
If you have time to work on it, it would be the prefered way to go.

[Aeliot-Tm]

Hi @Vincz!
Thank you for information. I'll have a look.

[Aeliot-Tm]

I created another more complex PR: #1040