Support `json` data type

[andyundso]

SQL Server 2025 adds a new JSON datatype:
https://learn.microsoft.com/en-us/sql/relational-databases/json/json-data-sql-server?view=sql-server-ver16#json-data-type

Previews are available for this new version:
https://www.microsoft.com/en-us/evalcenter/sql-server-2025-download

Would it be possible to add support for this new datatype in FreeTDS? I would expect that I can find out a column is of type JSON using dbcoltype. Don't know if anything more is needed, in terms of data it is still a string.