[Discover] Improve shard error message formatting (elastic#161098)

- Closes elastic#156645

## Summary

This PR updates UI of shards error modal.

### Updated design
<img width="500" alt="Screenshot 2023-07-07 at 10 05 00"
src="https://github.com/elastic/kibana/assets/1415710/a099a436-61fd-4522-b231-88a0d1179061">

![Jul-07-2023
10-20-13](https://github.com/elastic/kibana/assets/1415710/23069476-9aae-4c76-9e39-586a382dcf70)



### Before
<img width="500" alt="image 2"
src="https://github.com/elastic/kibana/assets/4016496/d3c067d9-2d18-4fcc-8db0-573defcb9b44">


For testing, please follow instruction from
elastic#41649 and drop `targetfield` on
Lens page.


### Checklist

- [x] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [x] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

---------

Co-authored-by: Andrea Del Rio <delrio.andre@gmail.com>
Co-authored-by: Stratoula Kalafateli <efstratia.kalafateli@elastic.co>