Add comprehensive analytics tracking

[xingyaoww]

This PR adds comprehensive analytics tracking for user entry points and first message:

• Added tracking for GitHub repository selection
• Added tracking for ZIP file upload
• Added tracking for first message after context (with entry point info)
• Added analytics documentation in docs/analytics.md

The changes will help us better understand how users enter and use the application.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:dbb3902-nikolaik   --name openhands-app-dbb3902   docker.all-hands.dev/all-hands-ai/openhands:dbb3902

[amanape]

Something seems wrong with the conflict resolver. The chat interface has been moved (https://github.com/All-Hands-AI/OpenHands/blob/main/frontend/src/components/features/chat/chat-interface.tsx) and this PR is trying to create a new one in its old place.

[xingyaoww]

I tried to manually resolve merge conflict and it seems OpenHands did a way better job than me do 😓

[enyst]

The initial post says:

Added analytics documentation in docs/analytics.md

The PR didn't add this, though. Was it forgotten or postponed? @xingyaoww