ACCESS-OM3 QA checks

[dougiesquire]

This issue is to keep track of QA checks to be added to model_config_tests/qa/test_access_om3_config.py.

Here's a list of things that were originally proposed to be added as checks in the Payu driver, but in the first instance many could be QA checks: https://github.com/COSIMA/access-om3/issues/109

[dougiesquire]

Also, check that ocn_cpl_dt in the nuopc.runconfig is consistent with the actual coupling timestep in nuopc.runseq