Update the values.yaml to include all possible settings.

[jgwerner]

Update the values.yaml so that it includes all possible settings for the end-user.

The values.yaml should have inline comments to document what each setting is for, in addition to the documentation provided in the README.md.

For example, the option to set the graderSpawnerMemLimit in the values.yaml file isn't there. Although the chart enforces a default, the end-user won't know that this setting is an option just by looking at the values.yaml file.