Add decorators or some form of metadata to allow more granular checks

[jacobgardner]

Is your feature request related to a problem? Please describe.
JSON schema allows validation of things that typescript doesn't care about such as string line length. We may want to investigate ways to allow these sorts of checks.

Describe the solution you'd like
I was originally thinking using decorators on fields to do the validation like string length, but we'll get syntax errors for decorators on interface fields or the interface itself, so I'm not sure what a good way of doing this is.