Add support for form arrays

[Christian24]

Hello,

I am excited about @tanstack/form. We are currently considering using it in a wrapper for lit.

Existing solutions like Formik or Angular's Reactive Forms have support for arrays as part of a dynamic form. This is Formik's documentation on what they call a Field Array: https://formik.org/docs/api/fieldarray.

I think @tanstack/form should offer something similar.

[Christian24]

Support seems to exist as in #492