Add owners for public facing API files (microsoft#15288)

### Description
Add owners for public facing API files

### Motivation and Context
Tighter control on the APIs

CODEOWNERS

@@ -20,3 +20,17 @@ requirements-training.txt @microsoft/onnxruntime-admin
 requirements.txt.in @microsoft/onnxruntime-admin
 /cgmanifests/cgmanifest.json @microsoft/onnxruntime-admin
 /cgmanifests/generated/cgmanifest.json @microsoft/onnxruntime-admin
+
+# Public facing APIs
+# C/C++
+/onnxruntime/include/onnxruntime/core/session/onnxruntime_c_api.h @microsoft/onnxruntime-api
+/onnxruntime/include/onnxruntime/core/session/onnxruntime_cxx_api.h @microsoft/onnxruntime-api
+/onnxruntime/include/onnxruntime/core/session/onnxruntime_cxx_inline.h @microsoft/onnxruntime-api
+
+# C#
+/onnxruntime/csharp/src/Microsoft.ML.OnnxRuntime/*.cs @microsoft/onnxruntime-api
+
+# Python
+/onnxruntime/onnxruntime/python/*.h @microsoft/onnxruntime-api
+/onnxruntime/onnxruntime/python/*.cc @microsoft/onnxruntime-api
+/onnxruntime/onnxruntime/python/*.py @microsoft/onnxruntime-api