Add StoreCreditQuery & Metafield Translations Field

A new root query, storeCreditConfiguration, returns a StoreCreditConfiguration object containing the non‑nullable Boolean field storeCreditEnabled, which indicates whether store credit is enabled for the shop. Developers can use this flag to conditionally display store‑credit UI or enable related business logic. The StoreCreditConfiguration type has no other fields and is newly introduced. The Metafield type is extended with a required translations field that returns a list of Translation objects. The translations field accepts a non‑nullable locale (String) argument and an optional marketId (ID) argument, allowing callers to filter translations by language and market. These changes add functionality for checking store credit status and retrieving localized metafield translations; no existing queries, mutations, or types are removed or deprecated.