add ticket number (and perhaps record locator) to tickets table

[AndrewBrook-Google]

the tickets table should probably have a unique ID that can be used when performing a deletion

to make things even more realistic, we might want to try to model the PNR codes (the 6-digit alphanumeric strings often called record locators) but that might be overkill

if you're curious, way way more info here: https://www.altexsoft.com/blog/pnr-explained/