temporal_reduction reduce all arrays by default

[burlen]

For the sake of usability it's desirable to defaulting to reducing all arrays (see #753). This should be implemented in the applicaiton in response to a user not passing a list of point arrays on the command line. In that case run the metadata phase of the pipeline and add the detected arrays to both the CF writer and tempral_reduction pipeline stages. Note: the temporal_reduction may need some refactoring to handle 2D and 3D data simultaneously.

[taobrienlbl]

a quick follow-up: I think that the temporal reduction does already correctly handle 2D and 3D data simultaneously. I've been using it to composite a bunch of ERA5 fields, including both 2D and 3D fields, and it is generating sensible results.

[burlen]

Looking at the cpp app I confirm that is the indeed the case.