stac/pipetask currently require the user to create a label explicitly in order to provide config overrides. We should make the default label to the Task class name (i.e. the same name that was just passed to -t). While it's possible to to have multiple instances of the same Task, that's currently quite rare and we should make the common case simpler and more intuitive.
After a bit of discussion, Nate Lust, Yusra AlSayyad, and I agreed it'd be better to use the Task class name rather than Task._defaultName because the former is what's also typically present on the same command line.