chore: Add denylist for elements_chain (#19193)

Getting ready to flip from allowlist to denylist.  Will run with both over the weekend, then will switch to denylist only.

posthog/api/decide.py

@@ -230,7 +230,14 @@ def get_decide(request: HttpRequest):
                     if random() < settings.NEW_ANALYTICS_CAPTURE_SAMPLING_RATE:
                         response["analytics"] = {"endpoint": settings.NEW_ANALYTICS_CAPTURE_ENDPOINT}
 
-            if settings.ELEMENT_CHAIN_AS_STRING_TEAMS and str(team.id) in settings.ELEMENT_CHAIN_AS_STRING_TEAMS:
+            if (
+                settings.ELEMENT_CHAIN_AS_STRING_TEAMS
+                and str(team.id) in settings.ELEMENT_CHAIN_AS_STRING_TEAMS
+                and (
+                    settings.ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS is None
+                    or str(team.id) not in settings.ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS
+                )
+            ):
                 response["elementsChainAsString"] = True
 
             if team.session_recording_opt_in and (

posthog/api/test/test_decide.py

@@ -3019,6 +3019,22 @@ def test_decide_element_chain_as_string(self, *args):
             self.assertEqual(response.status_code, 200)
             self.assertFalse("elementsChainAsString" in response.json())
 
+        with self.settings(
+            ELEMENT_CHAIN_AS_STRING_TEAMS={str(self.team.id)}, ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS={"0"}
+        ):
+            response = self._post_decide(api_version=3)
+            self.assertEqual(response.status_code, 200)
+            self.assertTrue("elementsChainAsString" in response.json())
+            self.assertTrue(response.json()["elementsChainAsString"])
+
+        with self.settings(
+            ELEMENT_CHAIN_AS_STRING_TEAMS={str(self.team.id)},
+            ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS={str(self.team.id)},
+        ):
+            response = self._post_decide(api_version=3)
+            self.assertEqual(response.status_code, 200)
+            self.assertFalse("elementsChainAsString" in response.json())
+
 
 class TestDatabaseCheckForDecide(BaseTest, QueryMatchingTest):
     """

posthog/settings/ingestion.py

@@ -40,3 +40,4 @@
 NEW_ANALYTICS_CAPTURE_SAMPLING_RATE = get_from_env("NEW_ANALYTICS_CAPTURE_SAMPLING_RATE", type_cast=float, default=1.0)
 
 ELEMENT_CHAIN_AS_STRING_TEAMS = get_set(os.getenv("ELEMENT_CHAIN_AS_STRING_TEAMS", ""))
+ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS = get_set(os.getenv("ELEMENT_CHAIN_AS_STRING_EXCLUDED_TEAMS", ""))