[SLO] Investigate query performance

[kdelemme]

Summary

When we create an SLO, the underlying transforms can potentially triggers some circuit breaker if the source query performs badly. Which can bring the cluster to a halt.

Let's investigate how we could measure the performance of the queries behind a SLO. Then we could think of a way to inform the user about this performance, and suggest a way to mitigate it.

Ideas:

• Based on the SLO configuration, generate the composite aggregate query, run it for a small window: look into the duration to execute the search query, and the number of pages yield by the composite.
• Get a color status: green, yellow, red indicating performance of the query.
• Show this on the SLO form.

[elasticmachine]

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

[elasticmachine]

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