Adding Index Configuration for Search in Synthetics Interface in Kibana

[b2ronn]

Description: Within our organization, we use Kibana with a large number of spaces, where each team conducts their synthetic tests(each team is limited by the indexes of its own space only). However, when reviewing test results through the Synthetics interface, delays occur due to inefficient searching in indexes {"index":"synthetics-*"}. This is particularly critical for supervisors who require access to multiple spaces./indexes.

Describe the feature: We propose adding functionality to the Synthetics interface similar to the "Uptime indices" option in the "Uptime Monitors" interface, allowing users to override indexes for search. This will optimize the process of searching test results and reduce the time needed to view synthetic test data.

Describe a specific use case for the feature:

1. The user accesses the Synthetics interface in Kibana.
2. A new option "Synthetics indices" appears in the interface settings.
3. The user can select indexes in which the search for test results will be performed.
4. After saving the settings, the Synthetics interface starts using the selected indexes for searching test data.
5. Supervisors and other users can more effectively review synthetic test results without unnecessary delays.

[elasticmachine]

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

[elasticmachine]

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