[UnifiedDataTable] Align header row configuration to Lens

[kertal]

In Lens users can configure the header row to show multiple lines. This is beneficial for long fieldnames which are very common in the works of o11y and beyond. When users have multiple columns configured with eg. lots of fieldnames starting with the same prefix (Like kubernetes....), this hides the most relevant information to distinguish between those fields.

Here's an example for this:

For consistency with Lens we should align configuration options, so users can change the header row to their need, allowing to see more of the field name at one sight when needed

When Discover consumes this change, its setting should be saved in the Save Search Saved Object.

Out of scope but worth to consider

• The default of showing 1 line should stay the same, we might consider changing the default in Discover but we should consider to align with Lens. If we change the default setting we need to consider other consumers of the package, to omit breaking changes.
• Given the need for multiline headers, it could make sense to integrate this into "EuiDataGrid", this has been requested before: [EuiDataGrid] Allow multi line headers eui#5536

[elasticmachine]

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

[teresaalvarezsoler]

@kertal being able to configure is great but I think it's hard to discover it. It's not the same in Lens because users are in this "creator mode" in which they know they can change how things look like. I strongly think we should have a better default such as the 3 lines + truncation. Regardless of making this issue, can we merge that other PR too?

[kertal]

Thx @teresaalvarezsoler for your feedback, how about discussing this in our next team sync?

[mbondyra]

As we decided that we want to have default 3 lines instead of 1, we have to think about how to redesign this tooltip option. Something to have in mind @andreadelrio @MichaelMarcialis

We could have 2 options: 'auto fit' or 'custom' and have custom set to 3 lines by default. Another option would be to rename single to default but this is a little vague.

[davismcphee]

@mbondyra Just a note that the approach we use in Discover for our default cell row height (3 rows) is to have "Custom" selected by default and set to 3.

[MichaelMarcialis]

+1 to what @davismcphee suggests here. That was exactly my expectation (Custom with 3 line selected by default).