chore: add type hint check (#840)

Author: leahecole

synthtool/gcp/templates/python_samples/noxfile.py.j2

@@ -39,6 +39,10 @@ TEST_CONFIG = {
  # You can opt out from the test for specific Python versions.
  'ignored_versions': ["2.7"],
 
+ # Old samples are opted out of enforcing Python type hints
+ # All new samples should feature them
+ 'enforce_type_hints': False,
+
  # An envvar key for determining the project id to use. Change it
  # to 'BUILD_SPECIFIC_GCLOUD_PROJECT' if you want to opt in using a
  # build specific Cloud project. You can also use your own string
@@ -132,7 +136,10 @@ FLAKE8_COMMON_ARGS = [
 
 @nox.session
 def lint(session):
- session.install("flake8", "flake8-import-order")
+ if not TEST_CONFIG['enforce_type_hints']:
+ session.install("flake8", "flake8-import-order")
+ else:
+ session.install("flake8", "flake8-import-order", "flake8-annotations")
 
  local_names = _determine_local_import_names(".")
  args = FLAKE8_COMMON_ARGS + [