docs: add error and schema management guides

[sarahxsanders]

Adds last TWO guides for the GraphQL production guide improvements:

• guide 1 is on error handling and debugging + includes format errors, custom error types, debugging production issues, and error recovery
• guide 2 is on schema management + covers schema evolution and governance w/ versioning safely, detecting breaking changes, deprecation workflows, governance processes, and other considerations

[vercel]

@sarahxsanders is attempting to deploy a commit to the The GraphQL Foundation Team on Vercel.

A member of the Team first needs to authorize it.