Fix midi generator cli

[SleepyLGod]

• Spring-boot framework configured.
• The fuctions dealing with mp3 files passed:
  • With input and output paths given and fixed, local mp3 files can be converted to midi files.
  • With input and output paths given and can be changed, the mp3 file transferred by the frontend can be downloaded and converted to local midi files.
• common configuration and self-created generic return objects and exceptions.
• Network cross-domain configuration.
• API documentation like swagger configuration.