fix: context params and pass req and res in an object

[Weakky]

closes #506

• Fixes a post apollo server integration issue regarding the context. We were no longer passing the req as first parameter, but an object with req
• Took that opportunity to refactor and pass the res as well as requested since quite a while by users. I know we said we didn't want addToContext to become a way to create server middleware and thus the res didn't make a lot of sense. Still, we left that issue for months now and the priority is still not there, so I figured out adding it now would be best.

TODO

• docs
  • jsdoc
  • website api
  • website guides
  • website tutorial
  • breaking changes
• tests

BREAKING CHANGES:

• The function passed to schema.addToContext (known as a "Context Adder") no longer has its first parameter being the request object. Instead it now receives an object (known as the "Context Adder Lens") containing the request object. In addition, on this lens, the response object can also be found. The lens exposes the request and response objects on properties req and res respectively. If you feel strongly that they should be request and response or any other thoughts you have please let us know on the issue tracker!

  before:

  schema.addToContext((req) => {
    // do something
  })

  after:

  schema.addToContext(({ req, res }}) => {
    // do something
  })

[jasonkuhrt]

Thanks for your pragmatism. Agree developers have waited too long for improvement here. Please document the breaking change (also make it part of the commit message). When we polish the release notes we'll copy-paste it.

[jasonkuhrt]

🙌