suggest support customize command to execute or support docker save -o ***.tar.gz ** to save image to dist

[H-TWINKLE]

suggest support customize command to execute such as:

setting:
  commands:
    - docker save -o ***.tar.gz ** 
    - docker tag **

or support docker save -o ***.tar.gz ** in settings plugin args

i want to save a image tat.gz file to drone/src, thanks !