Support for Struct type datatype in SQL endpoint

Currently complext type (json, struct) are supported in Onelake endpoint but not in SQL endpoint which prevents these important payload data types to be explored or used in Power BI. In big data world such fields are very common as many data generated through IoT are partially parsed in individual columns and raw json payload is left for future use or as on need basis.

Before parquet - we use to store them as MapType which make them easy to further use. Adding this feature will do both - parsing those field easy for end user and also migration of existing data possible.