Add --file to `sqlcmd open ads`, e.g. sqlcmd open ads https://aka.ms/AdventureWorks.sql

[stuartpa]

After doing sqlcmd create --using https://aka.ms/AdventureWorks.bak, it would be nice to bring up ADS with a .sql file that enables students/lab attendees to start exploring the database, enable:

sqlcmd open ads https://aka.ms/AdventureWorks.sql