Search for config directory up the tree

Right now if you change into some subdirectory and run modelbench or modelgauge, it will look for a config directory only in the current directory. If there isn't one there, it creates a sample one and then usually fails out because of missing keys. The result of this is a lot of spurious config directories that have to be cleaned up.

What I'd like it to do is look up the directory stack. So if I'm in /home/william/projects/modelbench/experiments/french/runs and I run modelgauge run-csv-items it should look first in the current directory and then up at least as far as modelbench for a config directory with secrets.yaml, and possibly all the way up.

This is mainly in aid of creating analytics tools that are easier to use.

Start by tracing how modelbench and modelgauge currently locate the config directory when invoked from the current directory. Verify the lookup behavior from a nested path such as experiments/french/runs, including discovery of config/secrets.yaml in an ancestor and avoiding creation of a spurious sample config when one exists above.