job_extra, extra and env_extra naming could be improved

[lesteve]

• job_extra -> job_header_extra
• env_extra -> job_script_extra? Not great, better suggestions welcome! Not sure if there is a good way to indicate that this is something which is at the beginning of the script but after the shebang and job header (and before we run dask-worker).
• extra -> dask_worker_additional_args, better suggestion welcome!

We may want to want to warn for a few releases and point to the new name parameter names, same thing for values from the config job-extra and env-extra if they are used.

[guillaumeeb]

I agree that the naming is not ideal, but do we really want to modify it? I'm not sure...

That said, that's not a strong opposition.

In batchspawner, env_extra is called prologue, https://github.com/jupyterhub/batchspawner/blob/master/batchspawner/batchspawner.py#L507.

[mrocklin]

We can always make a choice to break many APIs, and announce a major version bump.

Most dask-jobqueue users today are early adopters, and would probably be tolerant of such an action. It might be worth thinking about what other API changes we might want to make.

[lesteve]

This seems another candidate for breaking API changes, we have both mem and memory in LSFCluster:
#205

[riedel]

One could easily have both and add a deprecation warning, so I would argue that there could be coexisting until a major bump.

[guillaumeeb]

👍