Method GetTreeGroupBySqlPreviewAsync<TProps>(TreeQueryContext<TProps>, IEnumerable<GroupFieldRequest>, IEnumerable<AggregateRequest>)

Get SQL preview for tree GROUP BY query.
Base implementation: returns placeholder, override in Pro for actual SQL.

public virtual Task<string> GetTreeGroupBySqlPreviewAsync<TProps>(TreeQueryContext<TProps> context, IEnumerable<GroupFieldRequest> groupFields, IEnumerable<AggregateRequest> aggregations) where TProps : class, new()