docs(templates): add explanatory comment for has_auto_populated_fields in client templates

Author: hebaalazzeh

packages/gapic-generator/gapic/templates/%namespace/%name_%version/%sub/services/%service/async_client.py.j2

@@ -4,6 +4,8 @@
 {% import "%namespace/%name_%version/%sub/services/%service/_client_macros.j2" as macros %}
 {% import "%namespace/%name_%version/%sub/services/%service/_shared_macros.j2" as shared_macros %}
 
+{# Check if any method in this service has auto-populated fields (e.g. AIP-4235 request_id)
+   so setup_request_id is conditionally imported from _compat only when needed. #}
 {% set has_auto_populated_fields = namespace(value=false) %}
 {% for method in service.methods.values() %}
   {% set method_settings = api.all_method_settings.get(method.meta.address.proto) %}

packages/gapic-generator/gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2

@@ -6,6 +6,8 @@
 {% import "%namespace/%name_%version/%sub/services/%service/_client_macros.j2" as macros %}
 {% import "%namespace/%name_%version/%sub/services/%service/_shared_macros.j2" as shared_macros %}
 
+{# Check if any method in this service has auto-populated fields (e.g. AIP-4235 request_id)
+   so setup_request_id is conditionally imported from _compat only when needed. #}
 {% set has_auto_populated_fields = namespace(value=false) %}
 {% for method in service.methods.values() %}
   {% set method_settings = api.all_method_settings.get(method.meta.address.proto) %}