Index pattern creation UX: Surface time fields loading state

[cjcenizal]

Show loading indcator

Per @alexfrancoeur, we should display a loading indicator while the indices are being matched to the pattern, because it can sometimes take a few seconds between the time an index pattern is entered and the time fields showing up in the dropdown.

While it's loading, the time field dropdown should be disabled.

If this indicator is a little spinner next to the dropdown, then we could turn it into a little checkmark to indicate that the fields have been loaded.

Retrieve time fields as you type

Currently, the request to load the time fields is sent once the text input is blurred. This is a strange interaction, because you don't usually think of blurring something as an imperative action. Instead, we should send a debounced request as you type, so the information the user needs is retrieved as immediately as possible.

[thomasneirynck]

we will be able to reuse the loading-spinner component also in Visualize, for when there is idle time between data-retrieval and showing the result.

[alexfrancoeur]

@cjcenizal would it be possible to build as a generic component for the UI framework? There are plenty of areas we could use this when there is a delay in data-retrieval.

[cjcenizal]

@alexfrancoeur @thomasneirynck Absolutely! Per #9708 we will build every UI component to be as reusable as possible.

[cjcenizal]

Addressed by #13454