Support non-ts pool keys

[mattnibs]

If I create a pool with a pool key that isn't named ts, the app fails to show any data.

Steps to reproduce:

1. create pool with a non-standard pool key

$ zed create -orderby created_at:desc prs

2. add data

$ zq https://api.github.com/repos/brimdata/zed/pulls\?state\=all\&sort\=desc\&per_page=100 \
| zed load -use prs@main -

3. Run zed serve:

$ zed serve

4. Open Brim and observe that you don't see any data:

Brim appears be issuing a query that assumes the Pool key is ts when in this case it is the field created_at.

Observed in the dev console:

[jameskerr]

Thanks Matt. Will fix

[philrz]

This was fixed some time ago. The repro steps are repeated in Brim commit 290f138 in the attached video. This shows that the app now displays the data despite the non-ts pool key. Because the data is a top-level array, the default Table view shows a message about how it can't display it currently, but the Inspector view shows it fine, and some simple preprocessing Zed like over this makes it table-ready.

https://user-images.githubusercontent.com/5934157/185269909-078e9519-5e84-4c17-a820-868849a90002.mp4

Closing as fixed.