Designate an int enum as "Flags"

[Some languages have decorators](https://learn.microsoft.com/en-us/dotnet/api/system.flagsattribute?view=net-7.0) that can add functionality to enums that are meant to be a set of bit fields. Will [CADL enums](https://microsoft.github.io/cadl/docs/language-basics/enums/) support a decorator for enums so that language generators can take advantage of this?