[Actionable Observability] [SLO] Handle time-slice budgeting method

[kdelemme]

📝 Summary

Part of #137323

The goal is to add support for time-slice budgeting method. A time slice budgeting method requires a time slice target along side the slo objective target, as well as a time slice window. This can be added within the slo objective object as suggested by the OpenSLO project.

When computing the SLI data with the SLIClient, the query needs to aggregate per slice window and compute the ratio of good and total events compared to the time slice target to mark the slice as good or bad.
On top of the error budget consumption, we can return these values as minutes consumed and minutes remaining, since we know how many total slices there is during an slo time window, and how many are currently good.

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)