Overhaul the HPC chapter

[wlandau]

• Just feature the "clustermq", "future", and "hasty" backends. The others will be removed later on via Remove all non-clustermq parallel backends? ropensci/drake#561.
• Document the optional resources list column in the plan (Also update the list of possible columns in the chapter on plans.)

[kendonB]

I see this is closed - however, I can't see the documentation on the "optional resources list column in the plan"

[wlandau]

I omitted it before because I was having trouble getting it to work: futureverse/future.batchtools#26 (comment). You reminded me just now to try again, and I found the problem: futureverse/future.batchtools#26 (comment). Now I think I can add it.

[wlandau]

Fixed in 14858f4. Please see the new section on the resources column for transient workers. It is a brand new feature, and I have not test-driven it much, so I expect some snags.