Specify a pool key/name when a pool is created

[philrz]

In the Zeek-centric era, Zed lakes were assumed to always be keyed by a field of type time called ts. But Zed now have the ability to handle keys of other data types and named fields.

The Zui app will need some kind of UX to allow these alternate keys to be specified by the user. There may also be the potential to use heuristics such that the user could allow one to be picked automatically based on a sampling of the data.

Since this implies some kind of UX where the user could pause to specify the key, we could take the opportunity to let the user specify other pool creation settings at that time, such as the pool name.