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                            --
--------------------------------------------------------------------------
...

openapi-diff-cli のレポート出力のエントリポイントから開始し、古い入力ファイル名と新しい入力ファイル名がレポート生成にどのように渡されるかを追跡します。Issue の古い JSON 入力と新しい JSON 入力で CLI を実行し、既存の変更ログを変更せずに、表示されたセクションに両方のファイル名がレポートに含まれていることを確認します。