Update CSET documentation to reflect cset-workflow simplifications

At least 2 recent issues have looked at updating the cset-workflow internal logic, and organisation of GUI layout, option env names etc.
https://github.com/MetOffice/CSET/issues/1317
https://github.com/MetOffice/CSET/issues/1306
This issue is required to ensure CSET documentation is updated to reflect the latest position for users ahead of next release.

A further issue is likely to further refine internal logic which may further impact on some documentation details (tbc).

### Describe the solution you'd like
In particular, https://metoffice.github.io/CSET/getting-started/workflow-run.html includes snapshots of GUI layout and associated text requires updating to reflect the various configuration options (highlighting the help/info within GUI as source of truth rather than replicating these details in the more static documentation).

Instructions in https://metoffice.github.io/CSET/getting-started/run_full_cylc_workflow.html will also require updating.

### Describe alternatives you've considered
This change will be required ahead of next release to avoid documentation getting out of date.

Start by reviewing issues 1317 and 1306, then compare the workflow-run.html and run_full_cylc_workflow.html pages with the current CSET GUI and configuration options. Update the GUI snapshots, explanatory text, and full-workflow instructions to match the latest position, treating help/info in the GUI as the source of truth. Done means both pages reflect the pre-release behaviour.

Written by the indexing model from the issue text.