Fix timespan subfield references in 'where' and 'order_by' arguments.

Thanks for sorting out this confusion.

@Tim Jenness, here's a small review that's just documentation fixes and an attempt to make error messages more helpful:

https://github.com/lsst/daf_butler/pull/865

I'm fairly confident there was no actual missing functionality in the misadventures that spawned this ticket, but some of the CLI docs were definitely wrong.

I've just tried to create a unit test that would reproduce the problem, and everything seemed to work.  I didn't find an exact how-to-reproduce in that Slack thread, but I did try both command-line and in-Python versions of queryDimensionRecords with order_by="timespan.end" and order_by="exposure.timespan.end".  Let's try to reproduce it again in a week when USDF is back up.

Afraid there's been no progress yet; I've just been busy with other things.

Hello Jim,

Is this issue been tested? any help with the where cause is helpful.