Limit the selected number of nodes when run cron

I had a bit of a go at porting this to D9/10. Not sure that we should call the parameter max_nodes_per_cron anymore, maybe it should be renamed to reference entities in general. publish and unpublish methods take the limit as the command, but default to 0 so the original invocation should continue to work (albeit with no limit).
Will iterate on this when I have the opportunity.

Thanks geoffreyr for opening the MR. Looks good so far, but I wonder if we can simplify it? The SchedulerManager publish() and unpublish() functions are never going to be called with varying values, it will always be the value set in the config options. So instead of adding a parameter, could you just get the setting at the start of the function?

Also, we could introduce a default of, say 1,000 (?) rather than 'everything' so that we automatically prevent problems if no limit has been set? The the processing could start at the $limit and then $remaining_limit would get deprecated, and the processing stop when it is <= 0. Just an idea, not actually proved this is right, but worth a try.

We will need test coverage too, but don't let that hinder your progress.