[Serverless UX] Add option to show EuiBetaBadge by the navigation item label

[formgeist]

Summary

In the current stateful navigation for Observability, we've added the ability to show a small badge to indicate either beta or new features added. The current Serverless navigation component does not support this.

Example of current Observability navigation with badges

Proposal for the Serverless navigation badges

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)

[tsullivan]

This ability should be possible with the SharedIX changes in #167555

[formgeist]

The recommendation in collaboration with the Platform UX team was to not include beta badges in the navigation but instead highlight it in the app itself, either in the Kibana header or elsewhere. This is to not clutter the navigation further with too many labels and badges.

[sebelga]

For info, with #167774 we add support for navigation panels. You can see in the screenshots that we will allow badges next to a navigation item label. This is currently only for the items in the panels but it could be extended to the main navigation if needed.