chore(ES-331): enhance sdk docs

[Razz21]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSDoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[WojtekTheWebDev]

@rohrig Changes added in #7075

[rohrig]

In unified, we have

One of the questions I've seen come up is: "How do I use getRequestHeaders with useSdk?
Can you please address this? Is it possible? Is it recommended? I see the comment now that says "In the browser, getRequestHeaders will return an empty object." Can we take this one step further and explain usage with useSdk, or if it's not recommended, why and what to do instead if a dev feels it's needed. 🙂 Thanks in advance