Add column does not work for nvarchar

[ericmuijs]

When using the function sqlserver__alter_relation_add_remove_columns for a new field with nvarchar type, a nvarchar(1) is created.
For any nvarchar field with lengths greater than 1 the resulting merge/insert will fail.

[MLSteinw]

I have also come across issues relating to nvarchar and the length of the field not being captured when using the get_column_in_relation function

[ericmuijsvanoord]

@cody-scott : this is still the case for the newest version. I can see if I can work on a fix.