Add Form component

[bazottie]

Large parts are copied from projects by @jurgenbelien and @velomovies

Changes

• Adds a Form component
• Adds a Form Block
• Adds server side form validation with API route

Associated issue

#113

How to test

1. Open preview link
2. Navigate to /en/form-block-demo/

Checklist

• I have performed a self-review of my own code
• I have made sure that my PR is easy to review (not too big, includes comments)
• I have made updated relevant documentation files (in project README, docs/, etc)
• I have added a decision log entry if the change affects the architecture or changes a significant technology
• I have notified a reviewer

[cloudflare-workers-and-pages]

Deploying head-start with    Cloudflare Pages

Latest commit:	4191aee
Status:	✅  Deploy successful!
Preview URL:	https://fbe1ecd3.head-start.pages.dev
Branch Preview URL:	https://feat-forms.head-start.pages.dev

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