[apm] Clarify how data is populated in the APM Infrastructure tab

[colleenmcginnis]

Description

Clarifies how data is populated in the Infrastructure tab for a selected service in the Applications UI. This PR also attempts to provide guidance on how to self-diagnose / troubleshoot when the Infrastructure tab does not have any data.

I searched through some GitHub issues and discussion threads in addition to the resources @lucabelluccini linked to in #4359, but I wasn't able to find much information on troubleshooting.

This PR definitely needs more work, but I thought I'd open it to have something for the product/dev teams to respond to. @roshan-elastic can you help me find a technical reviewer? @lucabelluccini does this align with what you were expecting when you opened #4359?

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Related issue

Closes #4359

Checklist

• Product/Engineering Review
• Writer Review

Follow-up tasks

Select one.

• This PR does not need to be ported to another doc set because:
  • The concepts in this PR only apply to one doc set (serverless or stateful)
  • The PR contains edits to both doc sets (serverless and stateful)
• This PR needs to be ported to another doc set:
  • Port to stateful docs: <link to PR or tracking issue>
  • Port to serverless docs: <link to PR or tracking issue>

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[roshan-elastic]

Hey @colleenmcginnis,

Thanks for this. Let me ask some of the team how this works - it was made a fair while ago.

@kpatticha / @jasonrhodes - Do you know who might be able to evaluate these docs which are explaining how the 'infrastructure' tab works in the service views?

Preview - Infrastructure Tab
Preview - No data shown in the infrastructure tab

[kpatticha]

@roshan-elastic

@MiriamAparicio would you be able to take a look at these documents? I believe you’re the best person to provide input since you worked on the infrastructure tab in the service views.

If your availability is limited, I’m happy to dig into the code and help out

[colleenmcginnis]

👋 @MiriamAparicio are you available to take a look at this PR? If not, @smith can you help me find a reviewer? Thanks!

[MiriamAparicio]

Hi @colleenmcginnis, sorry I missed this, I'll take a look tomorrow first thing

[MiriamAparicio]

LGTM, thanks 🌟

[MiriamAparicio]

I think it's good information to know which fields are queried to get the infrastructure data in APM

[colleenmcginnis]

@MiriamAparicio Can you confirm that this is all correct too?