[Bug] Replace ENUM with with select_from_array

[tabacitu]

Since ENUM doesn't work in Postgres and other DBMSs, we should:

• change the migration to use VARCHAR instead of ENUM for that column
• use the select_from_array field type instead, which works on all DBMs

Would prevent the demo from seeming "broken" for people who try it on PosgreSQL, SQLite, SQLServer, etc.