docs: Quickstart frontend developer docs

[jonas-hoebenreich]

What does this PR do?

This PR adds a quickstart frontend developer guide for in-app surveys. Goal is to have an overview over all available functions and link to the detailed documentation guides.

Fixes # (issue)

How should this be tested?

• check /docs/in-app-surveys/developer-quickstart

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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[github-actions]

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

[ShubhamPalriwala]

Hey! Thanks for opening the PR. We're currently planning to shuffle our Docs a bit in preparation for the next release! Once that's done, I'll make some minor changes in this so that it aligns with that and merge it. Thanks again 🚀

[jobenjada]

Great write up, clear and concise - thanks a lot! 🤓💪

As Shubhi said, we'll make minor changes to it as our tech changes, but for the time being it's great!