Start splitting up the cloud test suite

[jbusecke]

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[jbusecke]

I think I finally got this to run properly. I have converted the grid_label, variable_id, and experiment_id to fixtures that are defined via command line inputs. I use these to separate the tests into a matrix of GHA jobs.
I think I finally figured out how to conditionally fail certain combinations of parameters for each test, allowing for very fine grained control/documentation which cases do cause problems. The xfail-strict option also allows detection of problems just 'fixing themselves' e.g. via changes introduced to the raw data.

[jbusecke]

Just as a record. This in combination with the indirect=True option seem to have been the crucial parts to get this going.