[OneDiscover] Don't display empty fields as default columns

[kertal]

📓 Summary

To improve the display of search results, any default columns that are empty for a particular search should not be displayed. In DataView mode we currently have a logic to place empty fields in the “Empty fields” section, so this logic can be adapted for hiding empty columns. For example, if service.name is empty, it should not be shown as a column.

✔️ Acceptance criteria

• If any default columns are empty for a particular search, they should not be displayed in the results.
• Utilize the existing logic for handling empty fields in the “Empty fields” section to manage the hiding of empty columns in data view mode, make use of the all_columns fields using ES|QL

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[davismcphee]

We discussed this in our sync today and decided not to do it for now due to drawbacks with both the "empty fields" approach or basing it on the fetched results:

• Using the "empty fields" logic, we'd have to delay showing results in the grid until the additional field caps request completes, which we don't want to do, and it could still result in many situations where default columns are empty for the current search anyway. It would also make the behaviour between data view and ES|QL modes inconsistent and potentially confusing.
• Basing it on just the fetched results would be consistent between data view and ES|QL modes, but may be misleading to users since the removed columns could still have data for the current search, just not within the current result set. There are concerns this could affect users' trust in the functionality.

Also, work on the summary column may affect how we choose to handle this. Setting to paused for now, and we'll revisit later once we've decided how to handle the summary column combined with default columns.