fix: Remove str type constrain in Fn:FindInMap to avoid the issue of looking up number in a map

[dkphm]

Remove the restriction on str type when Fn:FindInMap is called.

Which issue(s) does this change fix?

#6975

Why is this change necessary?

To allow customer to start lambda locally.

How does it address the issue?

Customer cannot start lambda locally if the yaml template include a function Fn:FindInMap inside a timeout property.

What side effects does this change have?

N/A

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.