Add dataflow definitions for opentelemetry (DataDog#22875)

Add missing dataflow declarations inferred from integration source/config for logs, metrics, and events where applicable.

Author: alexeypilyugin

otel/assets/dataflows.yaml

@@ -0,0 +1,5 @@
+provides:
+  - id: otel-metrics
+    always_on: true
+    data_type: metrics
+    direction: inbound