Allow Instructors to specify a Base Autograding Image and then install specific libraries if necessary

[20wildmanj]

Instead of using an interface to upload a complete docker image, it might be easier on the instructors to be able to specify ceratin aspects such as a bad image os, base version and variants, so that in most cases instructors don't need to create their own custom docker images. See Gradescope's version of this below:

Also, it is possible for them to install packages using apt manually as well.