fix(api-gateway): guard root orderBy cube name capitalization

[Tyagiquamar]

Check List

• Tests have been run in packages where changes have been made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Issue Reference this PR resolves

Closes #11700

Description of Changes Made

In packages/cubejs-api-gateway/src/graphql.ts (getJsonQuery), the root orderBy handler was unconditionally capitalizing the cube name (capitalize(cubeName)). When querying a cube declared with a lowercase-first or snake_case name (e.g. orders, lowercaseOrders), this resulted in non-existent order paths (such as Orders.count) causing query resolution errors under the Tesseract planner.

This change checks whether the cube already exists in metaConfig under its un-capitalized name before falling back to capitalize(cubeName), aligning with the existing pattern used in whereArgToQueryFilters, getMemberType, and the per-cube orderBy handler.