Add not_match validator

[mattremmel]

This would be nice to have for me, specifically for cases where all inputs are valid except for a single case (Uuid::nil()), or where two fields can contain similar types of data, but they can't exactly match. I haven't spent much time looking at the internals, but i'd be willing to try to write the code if its feasible to do.

[xFrednet]

I like the idea if negating a validation. This would be the negation of the match validation if I'm right. The question is what syntax could be used. Do you have a suggestion how to write this? 🙃 @mattremmel

[mattremmel]

I was originally thinking just an inverted version of must_match, but as I think about it, I'm not sure if that is needlessly restrictive. Its probably possible to do a generic not(...), that would would allow for things like #[validate(not(length(min =1, max = 3)))], the downside being another level of parenthesis around everything, but gaining increased flexibility.

[Keats]

I'm not sure we want to add generic not. match is one that might need it but the other validator seem to not need it. I mean, how often do you need something like #[validate(not(length(min =1, max = 3)))]

[IniterWorker]

I second @Keats. This is not the way to go. This could be solved with a custom validator.