Update a porting in the Porting Embed

[timomeh]

• Renders a form to update the porting (currently still a single form, splitting the form in multiple steps is in an upcoming PR).
• Uses @modular-forms/preact for form state handling and validation. It has a much smaller footprint compared to react-hook-form + zod, and RHF doesn't work well with preact.
• Updates the porting after submit.
• Allows to use your own submit button, with a simple <button form="gigsPortingEmbedForm" /> anywhere on the page.
• Adds an event validationChange which returns true or false when the validation of the form changed.
• Adds an event submitStatus which sends the status when the porting is submitted:
  • { status: 'loading' }
  • { status: 'success', porting }
  • { status: 'error', error }