Changing the Zarr URL is annoying

[aganders3]

For some reason I can't select all and delete or start typing a new URL. I think this is because it's trying to update on every change. It may be a better experience if the user has to hit enter/return to fetch a new Zarr.

[andy-sweet]

One option I thought about is to use onBlur instead of onChange, which represents a lose-focus event: https://developer.mozilla.org/en-US/docs/Web/API/Element/blur_event

But that doesn't let you change the text because we're setting the value from the dataUrl React state, which doesn't get updated until that lose-focus event! There must be some sane workaround for this...