[feat] Add form library examples to example app

[suzubara]

Does your feature request relate to a specific USWDS feature?
No

Is your feature request related to a problem? Please describe.
This feature will demonstrate how to use ReactUSWDS form components integrated with common React form libraries.

Describe the solution you'd like
Add the following to the /example application:

• formik
• react-hook-form

Additional context
Initial discussion: #77

[haworku]

Already started to do this in #351 . Can add a react-hook-form example next.

[haworku]

@suzubara do we still think further work here is needed? I am feeling like formik examples are enough for now until we have concrete examples of someone struggling with integrating with some other form library.

[suzubara]

@haworku I do think it would be worth continuing to flesh these out, mostly as a proof of concept but also as testing grounds as we build more complex components such as ComboBox & DatePicker to ensure they expose the necessary props in order to integrate. I can update the issue to reflect a more defined set of requirements.

[haworku]

No more example app, no need for this ticket.