Provide immediate feedback on search

Search could display spinner immediately on keystroke/clear-search to give fast "feedback", even though actual search gets called later. for example
```clojure
(r/with-let [typing? (r/atom false)
clear-typing-after-debounce
(debounce (r/partial reset! typing? false) debounce-time)]
[:input {:on-search #(do ; reduced example
(reset! typing? true)
(clear-typing-after-debounce))}]
;; show spinner immediately when possible
(when (or @typing? searching?)
[spinner/small]))
```

_Originally posted by @aatkin in https://github.com/CSCfi/rems/pull/3193#discussion_r1362039024_

We could also consider adding support for using `enter` key or search button.

We should also test the accessibility of the result and make it so that it makes sense.