CPU time keys in gather_resource_info.py

[QLeB]

In https://github.com/LSSTDESC/gen3_workflow/blob/master/python/desc/gen3_workflow/gather_resource_info.py#L23 :
Many tasks do not register any "substep" in the metadata, so their only CPU time related keys are startCpuTime and endCpuTime.
Because they do not start with a capital letter, they are not catch by key.endswith(min_field) and therefore no value is returned.

[QLeB]

One solution is to use if not key.lower().endswith(min_field.lower()):
but it's not very nice.

[QLeB]

Another possibility is implemented here: https://github.com/lsst-dm/ProdStat/blob/6c71e967a5d26e78ba72e4da5534c5ec315e7d2d/python/lsst/ProdStat/GetButlerStat.py#L106