Method GetGroupBySqlPreviewAsync(long, IEnumerable<GroupFieldRequest>, IEnumerable<AggregateRequest>, string?)
Pro: SQL Preview for GroupBy with filterJson (legacy compatibility).
Note: filterJson is ignored - use FilterExpression overload for filtering.
public Task<string> GetGroupBySqlPreviewAsync(long schemeId, IEnumerable<GroupFieldRequest> groupFields, IEnumerable<AggregateRequest> aggregations, string? filterJson = null)