Feature Request: Ability to conditionally show non-required fields

Prerequisites

• I have read the documentation;
• In the case of a bug report, I understand that providing a SSCCE example is tremendously useful to the maintainers.
• Ideally, I'm providing a sample JSFiddle or a shared playground link demonstrating the issue.

Description

In a schema with many required and optional fields, it would be handy to be able to conditionally only show required fields, especially if few users ever need them.

<Form
    requiredOnly={true}

Even better would be the ability to filter fields using an arbitrary function, for example:

<Form
    filter={field => field.isRequired && field.description.includes("test")}

But that might be going overboard. Thanks for considering!