Add save_every_iter option

[klchen0112]

PR Type and Checklist

What kind of change does this PR introduce?

When saving a large number of samples, saving each batch repeatedly will consume a lot of time. I added an option to control whether generated samples are saved every epoch.

• [ ] FIX BUG
  • [ ] Check CURRENT and PREVIOUS ISSUES..
  • [ ] Check WORFLOW result after PR.
• [ ] ADD ATTACK
  • [ ] DEFAULT values of arguments should be given except model.
  • [ ] Classname should be given as CamelCase.
  • [ ] Python file name should be SMALL letters of the classname.
  • [ ] Add attack in init.py
  • [ ] Check supported_mode whether the attack supports targeted mode.
  • [ ] README.md should be updated.
  • [ ] Check WORFLOW result after PR.
• [x] Other... Please describe: