chore: Use TypeGuard to avoid unncessary type casts

[aahung]

Issue #, if available

Description of changes

This change will get rid of str() casting without these errors:

samtranslator/model/connector/connector.py:151: error: Argument 2 to "_get_resource_arn" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
samtranslator/model/connector/connector.py:153: error: Argument 3 to "_get_resource_role_name" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
samtranslator/model/connector/connector.py:155: error: Argument 2 to "_get_resource_queue_url" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
samtranslator/model/connector/connector.py:157: error: Argument 2 to "_get_resource_id" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
samtranslator/model/connector/connector.py:159: error: Argument 2 to "_get_resource_name" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
samtranslator/model/connector/connector.py:161: error: Argument 1 to "_get_resource_qualifier" has incompatible type "Optional[Any]"; expected "str"  [arg-type]
Found 6 errors in 1 file (checked 159 source files)

Description of how you validated changes

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.