DM-43477: Create pipeline yaml file to create calexp summary metrics from existing calexps' summary stats

[jrmullaney]

Enables the production and writing of metrics generated from an existing calexp's summary statistics.

[jrmullaney]

Following the merge of DM-43231, it was decided that it would be good if one could make metrics from existing calexps, rather than having to create new calexps to make the metrics. I don't think this is possible without a pipeline or config file (i.e., it can't be done with a pipetask -c command line parameter), since the calexpMetrics.py analysis tool needs to be imported.

Note the name change, though: I am no longer calling it core (or even extended) as it shouldn't be run automatically or semi-automatically.