script configurable required items

[johrstrom]

In the original comment below we're talking about what fields are required for submitting a job. At a minimum script and cluster must be populated to submit a job to any scheduler at any center.

However, at OSC, we'd also require an account. (unless you have a slurm default file which shouldn't be a prerequisite for most users)

So, let's add a configuration that specifies what fields cannot be removed in script#edit so that centers (like OSC) are always populating what they need when they make new scripts.

Originally posted by @johrstrom in #3095 (comment)