Make error message clearer when using unsupported column types #270
Description
We don't support NTEXT, TEXT, or IMAGE columns in Output bindings (they aren't supported by OPENJSON and are going to be deprecated).
https://github.com/Azure/azure-functions-sql-extension#known-issues
Currently if a binding with one of those is used it just gives a generic error similar to Incorrect syntax near '*' which isn't very helpful. We should detect when columns are of any of the above types and throw a specific exception explaining to the user what the issue is.