Add getter/setter of C# OrtEnv log level (#13402)
### Description
* Add getter/setter to access and update C# OrtEnv log level
* Add C API about updating ort env with custom log level to support the
setter above (Following [pybind
implementation](https://github.com/microsoft/onnxruntime/blob/952c99304a764328070ac6c07f510deec06dedf4/onnxruntime/python/onnxruntime_pybind_state.cc#L923-L924))
* Add test case to verify getter & setter
### Motivation and Context
* For C++/Python, the log level can be adjusted via OrtEnv, and this
feature is missing in C# binding
