Add GraphQL Operation Validation for Bulk Operations CLI

[ericlee878]

Resolves: https://github.com/orgs/shop/projects/208/views/34?pane=issue&itemId=139461468&issue=shop%7Cissues-api-foundations%7C1114 and https://github.com/orgs/shop/projects/208/views/34?pane=issue&itemId=139446074&issue=shop%7Cissues-api-foundations%7C1112

Why are these changes introduced?

Improves the validation and error handling for GraphQL operations in the bulk operations service.

Implementation Details

• Enhances GraphQL document validation to ensure exactly one operation definition is present (error handling for cases that don't have exactly one operation)
• Additional unit tests added that prove core automatically rejects malformed documents (we don't have to do this).
• Created new validateGraphQLDocument() function that consolidates all GraphQL validation in one place:
  • Validates exactly one operation definition exists
  • Validates --variables flag is only used with mutations
  • Checks if the operation is a mutation (returns boolean that is used later). This replaces the previous isMutation() function.

Testing

Unit tests in execute-bulk-operation.test.ts