RFC Custom error messages for TypeBox

[tinkermakar]

This is rather a Request for Comments for a feature I want to PR. I wonder if I should name the new TypeBox field message, errorMessage or something else. I am going to open the PR once there is feetback from maintainers.

Is your feature request related to a problem? Please describe.

There is no way to add custom error messages to the TypeBox resolver. E.g. my use case is a consent checkbox and rather than getting userConsent must be true for a consent checkbox I would need to display a user-friendly message like Your consent is required, but I can't. Alternatives like Zod and Yup have an easy message property for such cases, but TypeBox doesn't have one

Describe the solution you'd like

1. Reference a new field on TypeBox schemas that will hold the message. TypeBox itself throws no errors for additional fields, so it can be anything: message, errorMessage etc. I wan to go with message, but I would highly appreciate if you would comment on that.

2. Modify resolver to read that new field, something along those lines: Custom errors using TypeCompiler sinclairzx81/typebox#500 (comment)

Describe alternatives you've considered
No good alternatives other than switching to Zod