Allow users to override the default account at setup time

[DavidHuber-NOAA]

Description

This adds a new option to setup_expt.py, and adds a missing argument to generate_workflows.sh, to allow users to specify which HPC account they wish to use. It also allows users to specify the environmental variable HPC_ACCOUNT at setup time to specify the account. Documentation is updated to note the new feature.

Resolves #3124

Type of change

• Bug fix (fixes something broken)
• New feature (adds functionality)

Change characteristics

• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? YES
• Does this change require an update to any of the following submodules? NO

How has this been tested?

Setup experiments on Hera.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have documented my code, including function, input, and output descriptions
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added
• I have made corresponding changes to the system documentation if necessary

[aerorahul]

lgtm

[CoryMartin-NOAA]

Looks great, thank you for this! Just noting for future thought, the other two variables that I need to change often are HPSS_PROJECT and HOMEDIR, so we may want to think about how to make those modifiable also.