feat: introduce a new environment variable in order to disable Scarf analytics

[realethanhsu]

…le Scarf analytics in the unstructured library.

Summary

This PR introduces a new environment variable that allows users to disable Scarf analytics in the unstructured library.
By setting SCARF_NO_ANALYTICS="true", users will benefit from the following:

1. Data Protection: Disabling analytics helps safeguard user privacy and data security, as the unstructured library collect user data without explicit consent.
2. Improved Startup Speed: The application can start up faster, particularly in poor network conditions. The unstructured library's logger module sends a request during application startup, which can lead to a poor user experience if the network is unreliable. In fact, I encountered this situation, I could not start the application at all due to this issue. Because my computer cannot access https://packages.unstructured.io .
   See github:unstructured:about analytics for more info.

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Screenshots

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Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

Please add this env to docker/.env.example as well.

[realethanhsu]

Please add this env to docker/.env.example as well.

Done.