Allow for centralized configuration

[afeld]

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

I have separate notebooks for each assignment, but they are generally structured the same. This means copying configuration options across all of them.

Describe the solution you'd like

I'd like to be able to specify configuration options in a single place, ideally in a config file. CLI arguments would work as well.

Describe alternatives you've considered

The documentation references otter_config.json, which may solve this problem, but I'm not seeing any documentation about the possible values of that file.

Additional context

#395 may be related.

[chrispyles]

Documentation for the keys available in otter_config.json can be found here but I don't think this will do what you want -- this is a file generated by Otter Assign based on the configurations in your assignment config. I think allowing this to be specified in a separate file is a good idea.

[chrispyles]

Support for these files was implemented in #573. To use this functionality, specify a config_file in your assignment config:

# ASSIGNMENT CONFIG
config_file: assignment_config.yml