Add `withGraphQL` Filter

[adamkelso]

• Lookup GraphQL Spec
• Figure out what can be easily supported from a filter perspective
  • Some of the internal functions could make for an unfriendly API on the Guzzler side
  • If it can be done just off of the final query string, it should be fine, but will need some work on the API friendliness.
• Create a WithGraphQL filter file.
• Build out class and tests.
• May require the most complex __toString() method thus far.

[adamkelso]

For anyone watching the issues on this project, I've decided to postpone this enhancement indefinitely. There are a handful to reasons:

1. GraphQL is a pretty intense querying language to parse out and would require a host of classes to cover the different functionalities of the spec.
2. I honestly have not found anyone interested in having a GraphQL filter. Now, there may be users of the package who do want this functionality, but I've had far more requests for creating more learning resources in both the documentation and code samples that can go into an entire repository.
3. From my own experience, GraphQL is used almost exclusively by front-end developers, Facebook, and almost no one else. (Shrug) Again, I may be out of the loop, and I'm sure there's somebody out there that breaks the mold and wants to make requests from PHP to a GraphQL service, but I haven't found them yet.

If there is enough interest, this enhancement can come back, but for now I'm moving onto other tasks that will be more useful for a wider audience.