Go back to running bake as individual tasks rather than using rose bunch

### What problem does your feature request solve?
Running a full length trials for a single UKV parameter causes cset bake to run out of wall clock, with a message that the out of memory (OOM) killer has been run multiple times.

There is also the issue of user control. When tasks are grouped in to a bunch it is difficult to see which specific task has caused an issue.

### Describe the solution you'd like
I'd like to see the workflow to run the plotting in individual cylc tasks. This will allow more memory/wall clock for individual tasks and will allow users to intervene if a specific task fails.

### Describe alternatives you've considered
Changing the number of tasks that `rose bunch` runs at once. This would ultimately turn a bunch of parallel tasks in to sequential tasks and significantly slow down cset.