[SLO][Details] Alert visibility for SLOs with "group by" service.name and "service.name:*"

[iblancof]

Description

While exploring SLOs and experimenting with group by, I noticed a pattern in how alerts are displayed.

For an SLO defined with service.name:* and group by service.name:

• On the main SLO page, if no instance is selected, the alerts appear empty.
• When filtering by a specific instance, the alerts are displayed.

Since no instance is selected, I wonder if it would make sense for the alerts tab/counter to query all the relevant/affected services.

The example I used with service.name:* might not be a very common use case, but I imagine the same considerations could apply to other types of definition/grouping.

Instance:none	Instance: frontend

[elasticmachine]

Pinging @elastic/actionable-obs-team (Team:actionable-obs)

[kdelemme]

Whenever an SLO is defined with a groupBy and the user is looking at the SLO Details page without an instanceId selected, we should fetch all alerts related to that SLO regardless of the instanceId.