Check GraphQL schema in CI

[mrmr1993]

This adds a buildkite job to check that our GraphQL schema is up-to-date. This would have prevented #7838, as well as all of the other times the schema has become mismatched.

Checklist:

• Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them:

[O1ahmad]

May be worth temporarily modifying a file under src to verify the job and dependencies.

[aneesharaines]

!approved-for-mainnet