Document federation-api logger.timestampPrefix config

Author: Ndpnt

content/api/federation.en.md

@@ -36,7 +36,8 @@ The default configuration can be found in `config/default.json`. The full refere
         "to": "The address to send the email to in case of an error",
         "from": "The address from which to send the email",
         "sendWarnings": "Boolean. Set to true to also send email in case of warning. Default: false",
-      }
+      },
+      "timestampPrefix": "Boolean. Set to true to prefix the timestamp of the error message with the current date (in ISO 8601 format YYYY-MM-DDTHH:MM:SSZ); see below"
     }
     "port": "Port number on which the server will listen for incoming connections. Default: 3333",
     "basePath": "The base path for the API endpoints",
@@ -51,6 +52,10 @@ The default configuration is merged with (and overridden by) environment-specifi
 
 For development, in order to have a local configuration that overrides the existing config, it is recommended to create a `config/development.json` file.
 
+### Logging
+
+Setting `logger.timestampPrefix` to `false` can be useful when logs are being collected by a process manager (like PM2) that already adds timestamps to log entries. This avoids duplicate timestamps in the logs.
+
 ### `collections` configuration key
 
 The `collections` configuration key is an array containing URLs or specific collections. Each item in the collections array can be either a URL pointing to a JSON file containing Collections objects, or a Collection object.