In openapi-diff-cli add old and new filenames to the output

When using openapi-diff-cli we need to give and filenames.
It will be cool to have those filenames in the report output.

Before:

==========================================================================
==                            API CHANGE LOG                            ==
==========================================================================
                           API Name API
--------------------------------------------------------------------------
--                            What's Changed                            --
--------------------------------------------------------------------------
...

After:

==========================================================================
==                            API CHANGE LOG                            ==
==========================================================================
                           API Name API
--------------------------------------------------------------------------
old file: xxx.json
new file: yyy.json
--------------------------------------------------------------------------
--                            What's Changed                            --
--------------------------------------------------------------------------
...

Start at the openapi-diff-cli report output entry point and trace how the old and new input filenames are passed into report generation. Run the CLI with the issue's old and new JSON inputs, then verify the report includes both filenames in the shown section without changing the existing change log.