feat: Update to webonyx/graphql-php ^15

[L3tum]

Proposed changes

• I've updated the lib to version 15
• To note is that I also removed some of the filtering that was going on in FederatedSchemaPrinter. I had that in a local branch for a while because otherwise the whole thing wouldn't work with Apollo and that has been confirmed by a rep as well, so I included those changes in this PR.

How to test

• The usual I guess^^

Unit Tests

• [x] This PR has unit tests
• [ ] This PR does not have unit tests: why?

FYI I've seen the two other PRs open so idk if you want to include this change. I had to fork the repo anyways and thought I'd contribute back, but it's alright if you don't wanna merge it.