[8.11] [DOCS] Clean up APM UI docs (#169269) (#169411)

# Backport

This will backport the following commits from `main` to `8.11`:
- [[DOCS] Clean up APM UI docs
(#169269)](#169269)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

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Clean up APM UI docs (#169269)\n\nCloses
https://github.com/elastic/observability-docs/issues/3292\r\n\r\n##
Summary\r\n\r\nUpdates documentation related to the APM UI based on
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[x] Add beta admonition to
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Clean up APM UI docs (#169269)\n\nCloses
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Summary\r\n\r\nUpdates documentation related to the APM UI based on
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Co-authored-by: Colleen McGinnis <[email protected]>

docs/apm/infrastructure.asciidoc

@@ -2,6 +2,8 @@
 [[infrastructure]]
 === Infrastructure
 
+beta::[]
+
 The *Infrastructure* tab provides information about the containers, pods, and hosts,
 that the selected service is linked to.
 

docs/apm/spans.asciidoc

@@ -43,8 +43,9 @@ For example, quickly view:
 [[distributed-tracing]]
 ==== Distributed tracing
 
-If your trace sample timeline is colorful, it's indicative of a distributed trace.
-Services in a distributed trace are separated by color and listed in the order they occur.
+When a trace travels through multiple services it is known as a _distributed trace_.
+In APM, the colors in a distributed trace represent different services and
+are listed in the order they occur.
 
 [role="screenshot"]
 image::apm/images/apm-services-trace.png[Example of distributed trace colors in the APM app in Kibana]

docs/apm/traces.asciidoc

@@ -17,6 +17,10 @@ it's the collective amount of pain a specific endpoint is causing your users.
 If there's a particular endpoint you're worried about, select it to view its
 <<transaction-details,transaction details>>.
 
+You can also use queries to filter and search the transactions shown on this page.
+Note that only properties available on root transactions are searchable.
+For example, you can't search for `label.tier: 'high'`, as that field is only available on non-root transactions.
+
 [role="screenshot"]
 image::apm/images/apm-traces.png[Example view of the Traces overview in APM app in Kibana]