[Infra][APM] Create a service in apm_data_access to provide APM collected host names

[crespocarlos]

Summary

Infra has only one setting to define the index pattern. The index pattern can be as generic as metric-* which also includes APM indices. This makes it harder for UIs to properly work with APM data.

Eg: In the hosts view we need to consider only docs generated by the system module. We could apply a filter by event.module: 'system' but that would filter out APM docs and we need APM docs to make the filter by service.name work.

This ticket is to properly decouple APM from Infra and allow Infra to properly request APM data via apm_data_access plugin

sequenceDiagram
    participant HostsView as Hosts View
    participant InfraPlugin as Infra Plugin
    participant APMDataAccess as APM Data Access

    HostsView->>InfraPlugin: Request hosts
    InfraPlugin->>InfraPlugin: Retrieve filtered host names
    InfraPlugin->>APMDataAccess: Request filtered host names
    APMDataAccess-->>InfraPlugin: Return filtered host names
    InfraPlugin->>InfraPlugin: Merge and dedup host names
    InfraPlugin->>InfraPlugin: Collect metrics only for the hosts monitored by the system integration
    InfraPlugin-->>HostsView: Return monitored hosts with metrics

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Implementation hints

• Create a service that will return the host names from APM indices. The parameters it needs to accept are (this is just a proposal, but it's roughly what's needed):

{
  timeFrom: number
  timeTo: number
  query: QueryDslQueryContainer
  limit: number
}

Issues/Tasks

Beta Give feedback

1. Add issues here
2. [Infra] Move apm common types to a package #189649
   Team:obs-ux-infra_services backport:skip ci:project-deploy-observability release_note:skip v8.16.0 +5
   
3. [Infra] Move data fetching core to apm data access #189654
   Team:obs-ux-infra_services backport:skip ci:project-deploy-observability release_note:skip v8.16.0 +5
   

AC

• Service returns host names from APM docs

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