[docs]: OCI key_file path clarrification

[HysunHe]

This PR is to clarrify the key_file path configuration in the oci config file.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh

[Michaelvll]

I would prefer to handle this automatically in the code, instead of adding a comment. Do you think it would be hard to change in that way?

[HysunHe]

I would prefer to handle this automatically in the code, instead of adding a comment. Do you think it would be hard to change in that way?

Would prefer to change the code later after done merging the new provisioning API impl. We doc it before that?