chore: Add decorator @deprecated and add it to is_str()

[aahung]

Issue #, if available

Description of changes

Description of how you validated changes

Create a file "bin/test_deprecation.py" with the content:

from samtranslator.model.types import is_str

if __name__ == "__main__":
    is_str()("hi")

Then:

(samtranslator37) ~/P/serverless-application-model ❯❯❯ python bin/test_deprecation.py
bin/test_deprecation.py:4: DeprecationWarning: is_str is deprecated, please consider to use IS_STR
  is_str()("hi")

Checklist

• Adheres to the development guidelines
• Add/update transform tests
  • Using correct values
  • Using wrong values
• Add/update integration tests

Examples?

Please reach out in the comments if you want to add an example. Examples will be
added to sam init through aws/aws-sam-cli-app-templates.

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