Optionally add a column for the Allowed valies

[emanuele-leopardi]

Hello!

First of all thank you for this amazing piece of code.

I'd like to make a suggestion:

I think it would be pretty wild if it was possible to add another column optionally to set also the possible allowed values and not just the default one.

something like

Key	Type	Default	Description	Allowed Values
springFlyway.locations	string	"postgres"	if enabled: true this sets classpath:db/migration/<locations>	postgres,oracle