Fix/remove typing ext for py38 for repo

[nadobando]

Issue aws-powertools#280

Description of changes:

1. Added if block to know if typing_extensions should be imported based on the python version.
   if python >= 3.8 typing extensions will not be imported and the native implementation will be used
   else will try to import typing_extensions and catch the ImportError

2. Updated modules which imported this dependency.

3. Updated pyproject.toml to only install typing-extensions when python version is <3.8
   Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

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