feat: Add hiddenFields to app & website surveys

[gupta-piyush19]

What does this PR do?

Adds hidden fields to app & website surveys.

Fixes
https://github.com/formbricks/internal/issues/177

How should this be tested?

• Create a survey and add a few hidden fields to it.
• Use formbricks.track method to pass the hidden fields(inside properties) to the survey response.

 formbricks.track("my event", {
      hiddenFields: {
        myField: "my value",
      },
    });

Checklist

Required

• Filled out the "How to test" section in this PR
• Read How we Code at Formbricks
• Self-reviewed my own code
• Commented on my code in hard-to-understand bits
• Ran pnpm build
• Checked for warnings, there are none
• Removed all console.logs
• Merged the latest changes from main onto my branch with git pull origin main
• My changes don't cause any responsiveness issues
• First PR at Formbricks? Please sign the CLA! Without it we wont be able to merge it 🙏

Appreciated

• If a UI change was made: Added a screen recording or screenshots to this PR
• Updated the Formbricks Docs if changes were necessary

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2 Ignored Deployments

Name	Status	Preview	Comments	Updated (UTC)
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[github-actions]

Thank you for following the naming conventions for pull request titles! 🙏

[pandeymangg]

looks and works great! thanks for the PR mate, just added two small comments (nit), pls take a look

[mattinannt]

@gupta-piyush19 thanks :-) looks great in general. Only a few suggestions regarding the type naming and logs: