[FEAT] S3-compatible upload

[dragon-fish]

I hope the following features can be added to Milkdown:

1. Support uploading files to S3-compatible object storage
2. Support defining filename templates, e.g. uploads/{full_year}/{full_month}/{full_day}/{sha1}.{ext}

Thank you for your great work!

[LarryZhu-dev]

@dragon-fish 用户您好，
近期 milkup 正在代码重构整理，短时间内不会有功能更新和修复，请持续关注此 issue，将在有进展时在此通知您

[LarryZhu-dev]

@dragon-fish 此问题已进入日程，近期内将修复或支持。