Feature request: Implement the ExtraKeys method described in the Docs

[nCubed]

Use case

In the official docs, the Extra Keys example shows the AppendKeys method - looks to be a mistake in the docs.

We've discussed this in a discussion thread: #1035

Assuming the ExtraKeys are not actually implemented, I would recommend the operation be thread safe.

Solution/User Experience

Implementing the ExtraKeys method would eliminate the AppendKey/RemoveKey dance we currently have to use.

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