feat(opentelemetry): Add entry point for SentryPropagator (#3086)

Add entry point for sentry_sdk.integrations.opentelemetry.SentryPropagator.
This makes possible to configure opentelemetry using environment variables
and add SentryPropagator to existing ones instead of replace them.

Closes #3085

Co-authored-by: Neel Shah <neel.shah@sentry.io>

setup.py

@@ -131,6 +131,11 @@ def get_file_text(file_name):
         "starlite": ["starlite>=1.48"],
         "tornado": ["tornado>=6"],
     },
+    entry_points={
+        "opentelemetry_propagator": [
+            "sentry=sentry_sdk.integrations.opentelemetry:SentryPropagator"
+        ]
+    },
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Environment :: Web Environment",

tests/integrations/opentelemetry/test_entry_points.py

@@ -0,0 +1,17 @@
+import importlib
+import os
+from unittest.mock import patch
+
+from opentelemetry import propagate
+from sentry_sdk.integrations.opentelemetry import SentryPropagator
+
+
+def test_propagator_loaded_if_mentioned_in_environment_variable():
+    try:
+        with patch.dict(os.environ, {"OTEL_PROPAGATORS": "sentry"}):
+            importlib.reload(propagate)
+
+            assert len(propagate.propagators) == 1
+            assert isinstance(propagate.propagators[0], SentryPropagator)
+    finally:
+        importlib.reload(propagate)