feat: Default Inferred Services on for edxapp (#157)

It's on in stage, edge, and prod, but not sandboxes yet.

See edx/edx-arch-experiments#737

playbooks/roles/edxapp/defaults/main.yml

@@ -634,7 +634,7 @@ EDXAPP_DATADOG_PROFILING_ENABLE: "{{EDXAPP_DATADOG_ENABLE and COMMON_ENABLE_DATA
 # Inferred Services allows for unification of service names for all
 # spans in the webapp and faceting metrics by service.
 # https://docs.datadoghq.com/tracing/guide/inferred-service-opt-in/?tab=python
-EDXAPP_DATADOG_INFERRED_SERVICES_ENABLE: false
+EDXAPP_DATADOG_INFERRED_SERVICES_ENABLE: true
 # ddtrace 2.7.9 contains a fix for a pymongo incompatibility.
 # (Same fix is present in 2.8.2 on the 2.8.x release line.)
 EDXAPP_DDTRACE_PIP_SPEC: 'ddtrace>=2.7.9'