Add multi-turn conversation guidance to trace documentation

## Problem
The documentation lacks clear guidance on how to handle multi-turn user interactions (multiple requests + responses) within a single trace, as mentioned in user feedback.

## Files to Update
- docs/v2/concepts/traces.mdx
- docs/v2/usage/manual-trace-control.mdx

## Changes Needed
- Add comprehensive examples showing how to group multiple conversation turns in one trace
- Show how to use trace metadata to track conversation progress
- Provide best practices for multi-turn conversation patterns
- Include error handling for interrupted conversations

## Context
Users are struggling to implement multi-turn conversations where multiple requests and responses should be combined into one trace for better observability.

## Assignee
Please assign to Dwij when creating