docs: update form builder docs

[nlvcodes]

Simple updates to documentation after testing out the options for a video script.

BeforeEmail doesn't exist in '@payloadcms/plugin-form-builder' but it does in '@payloadcms/plugin-form-builder/types.' Importing anything from '@payload-types' doesn't work, as it should be '@/payload-types'

What?

Simple update to the documentation to correctly reflect where to find the BeforeEmail types. Also correcting a type that didn't include the proper file path to payload-types.

Why?

Clarification and fixing typos.