docs: updates to apm agent config (#61893)

docs/apm/agent-configuration.asciidoc

@@ -31,37 +31,18 @@ Kibana communicates any changed settings to APM Server so that your agents only
 [float]
 ==== Supported configurations
 
-[float]
-===== `CAPTURE_BODY`
+Each Agent has its own list of supported configurations.
+After selecting a Service name and environment in the APM app,
+a list of all available configuration options,
+including descriptions and default values, will be displayed.
 
-added[7.5.0] Can be `"off"`, `"errors"`, `"transactions"`, or `"all"`. Defaults to `"off"`.
+Supported configurations are also marked in each Agent's configuration documentation:
 
-For transactions that are HTTP requests, the Agent can optionally capture the request body, e.g., POST variables.
-Remember, request bodies often contain sensitive values like passwords, credit card numbers, etc.
-If your service handles sensitive data, enable this feature with care.
-Turning on body capturing can also significantly increase the overhead the overhead of the Agent,
-and the Elasticsearch index size.
-
-[float]
-===== `TRANSACTION_MAX_SPANS`
-
-added[7.5.0] A number between `0` and `32000`. Defaults to `500`.
-
-Limit the number of spans that are recorded per transaction.
-This is helpful in cases where a transaction creates a very high amount of spans, e.g., thousands of SQL queries.
-Setting an upper limit will help prevent the Agent and the APM Server from being overloaded.
-
-[float]
-===== `TRANSACTION_SAMPLE_RATE`
-
-added[7.3.0] A sample rate between `0.000` and `1.0`. Default configuration is `1.0` (100% of traces).
-
-Adjusting the sampling rate controls what percent of requests are traced.
-`1.0` means _all_ requests are traced. If you set the `TRANSACTION_SAMPLE_RATE` to a value below `1.0`,
-the agent will randomly sample only a subset of transactions.
-Unsampled transactions only record the name of the transaction, the overall transaction time, and the result.
-
-IMPORTANT: In a distributed trace, the sampling decision is propagated by the initializing Agent.
-This means if you're using multiple agents, only the originating service's sampling rate will be used.
-Be sure to set sensible defaults in _all_ of your agents, especially the
-{apm-rum-ref}/configuration.html#transaction-sample-rate[JavaScript RUM Agent].
+[horizontal]
+Go Agent:: {apm-go-ref}/configuration.html[Configuration reference]
+Java Agent:: {apm-java-ref}/configuration.html[Configuration reference]
+.NET Agent:: {apm-dotnet-ref}/configuration.html[Configuration reference]
+Node.js Agent:: {apm-node-ref}/configuration.html[Configuration reference]
+Python Agent:: {apm-py-ref}/configuration.html[Configuration reference]
+Ruby Agent:: {apm-ruby-ref}/configuration.html[Configuration reference]
+Real User Monitoring (RUM) Agent:: {apm-rum-ref}/configuration.html[Configuration reference]