fix: Use importlib.metadata.version() to remove implicit dependency on setuptools

[skirino]

Description

• Currently dbt-athena implicitly depends on setuptools as it imports pkg_resources.
• Use importlib.metadata instead to remove the implicit dependency.

Our context

• We are using bazel with rules_python in our project. We need to tell bazel the exact set of dependencies of our application (including commonly-used libraries such as setuptools).
• dbt-athena currently does not declare setuptools as a dependency, so bazel and rules_python do not know the fact that setuptools is needed in our application (which depends on dbt-athena). This leads to errors when loading dbt.adapters.athena.
• Adding setuptools as a dependency of dbt-athena in setup.py is a possible solution, but I think it's simpler to use the stdlib API and remove the dependency.

Models used to test - Optional

None

Checklist

• You followed contributing section
• You kept your Pull Request small and focused on a single feature or bug fix.
• You added unit testing when necessary : (the existing test already covers the changed code)
• You added functional testing when necessary