add feedback widget with posthog

[HarshCasper]

This PR:

• Implements a docs feedback system using PostHog Surveys
• Adds an API-based survey capture with "Was this helpful?" yes/no flow and optional text feedback
• Added contextual follow-up questions: positive feedback shows "What did you like?" options, negative shows "What went wrong?" options
• Styled widget for both light/dark modes with compact UI, radio buttons, and success state

[cloudflare-workers-and-pages]

Deploying localstack-docs with    Cloudflare Pages

Latest commit:	5244101
Status:	✅  Deploy successful!
Preview URL:	https://cd298726.localstack-docs.pages.dev
Branch Preview URL:	https://feedback-widget.localstack-docs.pages.dev

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[remotesynth]

As noted, please adjust the colors of the line and text to match.