feat(spans): Config stub for span.op inference (#77851)

Add a first rule to derive missing `span.op`s in Relay.

src/sentry/relay/globalconfig.py

@@ -7,7 +7,7 @@
     MetricExtractionGroups,
     global_metric_extraction_groups,
 )
-from sentry.relay.types import GenericFiltersConfig
+from sentry.relay.types import GenericFiltersConfig, RuleCondition
 from sentry.utils import metrics
 
 # List of options to include in the global config.
@@ -28,11 +28,21 @@
 ]
 
 
+class SpanOpDefaultRule(TypedDict):
+    condition: RuleCondition
+    value: str
+
+
+class SpanOpDefaults(TypedDict):
+    rules: list[SpanOpDefaultRule]
+
+
 class GlobalConfig(TypedDict, total=False):
     measurements: MeasurementsConfig
     aiModelCosts: AIModelCosts
     metricExtraction: MetricExtractionGroups
     filters: GenericFiltersConfig | None
+    spanOpDefaults: SpanOpDefaults
     options: dict[str, Any]
 
 
@@ -43,6 +53,25 @@ def get_global_generic_filters() -> GenericFiltersConfig:
     }
 
 
+def span_op_defaults() -> SpanOpDefaults:
+    return {
+        "rules": [
+            {
+                # If span.data[messaging.system] is set, use span.op "message":
+                "condition": {
+                    "op": "not",
+                    "inner": {
+                        "op": "eq",
+                        "name": "span.data.messaging\\.system",
+                        "value": None,
+                    },
+                },
+                "value": "message",
+            }
+        ]
+    }
+
+
 @metrics.wraps("relay.globalconfig.get")
 def get_global_config():
     """Return the global configuration for Relay."""
@@ -51,6 +80,7 @@ def get_global_config():
         "measurements": get_measurements_config(),
         "aiModelCosts": ai_model_costs_config(),
         "metricExtraction": global_metric_extraction_groups(),
+        "spanOpDefaults": span_op_defaults(),
     }
 
     filters = get_global_generic_filters()