Reduce severity & verbosity of instrumentation ImportError (#1115)

In auto-instrumentation context, it is expected that many of the supported target libraries will not be present.
Hence, it does not make sense to flood logs with ImportErrors for this expected scenario.

Author: john-karp

opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/_load.py

@@ -145,7 +145,7 @@ def _load_instrumentors(distro):
             # environment regarding python version, libc, etc... In this case it's better
             # to skip the single instrumentation rather than failing to load everything
             # so treat differently ImportError than the rest of exceptions
-            _logger.exception(
+            _logger.warning(
                 "Importing of %s failed, skipping it", entry_point.name
             )
             continue

opentelemetry-instrumentation/tests/auto_instrumentation/test_load.py

@@ -376,7 +376,7 @@ def test_load_instrumentors_import_error_does_not_stop_everything(
             ]
         )
         self.assertEqual(distro_mock.load_instrumentor.call_count, 2)
-        mock_logger.exception.assert_any_call(
+        mock_logger.warning.assert_any_call(
             "Importing of %s failed, skipping it",
             ep_mock1.name,
         )