[SLO] SLO group embeddable behaves differently in Serverless when no SLOs

[mgiota]

🍒 Summary

While testing the SLO Overview embeddable on stateful and serverless, I noticed a different UI experience in case there are no SLOs.

Serverless

When user has no SLOs and user adds a Group Overview embeddable group by status, a healthy group appears, stating there is 1 healthy SLO, which is wrong, since there are no SLOs.

https://github.com/elastic/kibana/assets/2852703/491f9b9d-9b9f-4b53-8eb4-cdfb68051e0a

Stateful

On Stateful, when user has no SLOs and adds a Group Overview embeddable group by status, No group results message appears.

https://github.com/elastic/kibana/assets/2852703/0044b0eb-38df-4dae-9d3c-86cda57699e6

✅ Acceptance criteria

• Serverless should behave similar to stateful and display the No group results message
• Unless we want to consider disabling the Save button in the SLO Group Overview configuration screen in case there are no SLOs

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)