Add noneof and noneofci validator to assert value is not within list of values #1552

Currently, validator supports oneof to assert that a string/int is within one of the allowed values: oneof=red green

Can we add a validator noneof to do the inverse of this? It would verify that the string does not match any the given restricted values: noneof=red green

noneofci would be the case-insensitive equivalent of this

I can help raise a PR for this if you're fine with me adding a validator for it