[AWSX] fix(logs forwarder): Update docs on trace forwarding

[ge0Aja]

What does this PR do?

• Update docs on trace forwarding indicating that the forwarder needs to be instrumented.
• Update enhanced metrics submission to use lambda_metric which automatically selects the handler based on what's available.
• The forwarder used lambda_stats.distribution directly which could be null sometimes depending on different factors like having the extension enabled.

Motivation

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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