Config docs update with note for AWS Lambda (#1720)

* Updated docs with a note about aws lambda configuration, see GH-1704 for more info.

* Update docs/configuration.asciidoc

LGTM

Co-authored-by: Colton Myers <[email protected]>

Co-authored-by: brett-fitz <[email protected]>
Co-authored-by: Colton Myers <[email protected]>

Author: 3 people

docs/configuration.asciidoc

@@ -115,6 +115,7 @@ or whitespace-only.
 
 The URL for your APM Server.
 The URL must be fully qualified, including protocol (`http` or `https`) and port.
+Note: Do not set this if you are using APM in an AWS lambda function. APM Agents are designed to proxy their calls to the APM Server through the lambda extension. Instead, set `ELASTIC_APM_LAMBDA_APM_SERVER`. For more info, see <<lambda-support,AWS Lambda>>.
 
 [float]
 [[config-enabled]]