Feature request: Metrics LMI support

[hjgraca]

Use case

With the new Lambda support for concurrent exectutions (LMI) we need to make Metrics thread-safe

Solution/User Experience

Thread-safe dictionary for per-thread context storage.
Uses ManagedThreadId as key to ensure isolation when Lambda processes multiple concurrent requests

Alternative solutions

Acknowledgment

• This feature request meets Powertools for AWS Lambda (.NET) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Python, Java, and TypeScript