Fix formData code snippet in route handler docs

[joulev]

Why?

The code snippet in the Route handler formData documentation

import { NextResponse } from 'next/server'
 
export async function POST(request: Request) {
  const formData = await request.formData()
  return NextResponse.json({ formData })
}

is slightly wrong, because formData is not a plain object and hence return NextResponse.json({ formData }) doesn't actually work.

Since we are already in the topic of parsing formData, I also added a mention on zod-form-data which can be used to validate the form and parse it to non-string formats such as number.

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: d3f0b78

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer