Able to specify image platform when creating ch shell

[camerondurham]

Is your feature request related to a problem? Please describe.

• camerondurham/cs350-docker commands fail (appears to be on any non-linux/amd64 arch system), see:
  • ch create for csci350 errors out, but run_scripts workflow works #47
  • ch create for csci350 errors out, but run_scripts workflow works for some people cs350-docker#15

Describe the solution you'd like

ch should offer specifying the image platform you want to run with a platform flag.

This issue covers the feature required to create a shell env and specify the platform, but the cs350-docker repo needs to have documentation updated too.

[a-harhar]

@camerondurham I've been working on this locally, fairly certain I figured out how to do it. I'll make the PR for it shortly!

[a-harhar]

@camerondurham created PR for adding the flag #49. Please leave any suggestions that you have on coding style and I can make the updates! Also not entirely sure if I updated all the places for documentation (I updated README but that was it). Hope this helps!