[Lens] Concatenation Aggregation on .keyword/string fields in Lens

[Jonas-268]

Describe the feature:
I'm missing the concatenation aggregation in lens which TSVB already has. Details and example: https://discuss.elastic.co/t/aggregate-by-concatenate-in-lens/341820

This would make it possible to give insights about which data went into a lens aggreagtion

Describe a specific use case for the feature:
We use Kibana among other things for HR Dashboards. There is one showing hours which are paid because of illness over time. One document contains fields with hours per month, wagetype and division. It also contains a string list of people responsible for the hours concatenated into a single field by the database query.
The Lens showing the information gives only hours per month compared to productive hours. There are control elements to filter by division or wagetype.

The new requirement is to show which people are responsible for the hours (I want to click on it and see the persons).
Lens has the expand button for big fields so if lens could aggregate by concatenating the string lists into one list, the problem would be solved. I could add another column which would dynamically update the list of people responsible for the hours when selecting different filters in the controls.

I already had this problem once before with a dashboard showing supplier sales. Overall it shows sales totals for suppliers over all our departments. Again someone was like: I want to see which departments went into the sum. My solution then was another second lens next to the first one that doesn't aggregate by department like the first one. So if you filter for a single supplier it will list the sales totals per department for that supplier in the second lens. Again this could have been a column with a concatenated string instead.

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)

[markov00]

In order to provide better transparency of priorities, issues that will not be prioritized within the next 24 months are being closed.

Tracking request in Lens general improvements ice box, solvable possibly with ESQL #184648