Add onnx output option for trt_compiler

[yiheng-wang-nv]

Fixes # .

Description

So far, it's onnx model is in a tmp folder and will be removed after execution. For users that need onnx model, it will be more convenient to add an option to save it to a specified path.

Types of changes

• [x] Non-breaking change (fix or new feature that would not break existing functionality).
• [ ] Breaking change (fix or new feature that would cause existing functionality to change).
• [ ] New tests added to cover the changes.
• [ ] Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• [ ] Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• [ ] In-line docstrings updated.
• [ ] Documentation updated, tested make html command in the docs/ folder.

[yiheng-wang-nv]

/build

[yiheng-wang-nv]

close as it's not needed