docs: add naming and design guide - #2279

Description

adds a new guide for the "schema governance" series on graphql.org/learn Includes new guide: Establish naming conventions and design standards:

• Field and type naming patterns
• Boolean field prefixes
• Mutation naming strategies
• Input/output type suffixes
• Nullability patterns and null bubbling behavior
• Schema documentation best practices
• Custom scalars for domain-specific types
• Error handling approaches
• Pagination with Relay connections
• Schema linting with GraphQL-ESLint
• CI/CD validation pipeline examples
• Common anti-patterns to avoid

PLEASE DO NOT MERGE, THIS IS PART OF A SERIES OF GUIDES ON SCHEMA GOVERNANCE. THERE ARE TWO MORE GUIDES TO FOLLOW

Note: this needs heavy technical review - the content is based on heavy research i did, but since there's no strict naming conventions/guidance defined in the schema we will want to proceed with confidence that everything here is guidance we want to put out there!