message: docs: add missing docs for access log %REQUEST_DURATION%
diff: @@ -216,6 +216,16 @@ The following command operators are supported:
  Renders a numeric value in typed JSON logs.
  +%REQUEST_DURATION%
  + HTTP
  + Total duration in milliseconds of the request from the start time to the last byte of
  + the request received from the downstream.
  +
  + TCP
  + Not implemented ("-").
  +
  + Renders a numeric value in typed JSON logs.
  +
  %RESPONSE_DURATION%
  HTTP
  Total duration in milliseconds of the request from the start time to the first byte read from the
  @@ -226,6 +236,16 @@ The following command operators are supported:
  Renders a numeric value in typed JSON logs.
  +%RESPONSE_TX_DURATION%
  + HTTP
  + Total duration in milliseconds of the request from the first byte read from the upstream host to the last
  + byte sent downstream.
  +
  + TCP
  + Not implemented ("-").
  +
  + Renders a numeric value in typed JSON logs.
  +
  .. _config_access_log_format_response_flags:
  %RESPONSE_FLAGS%
  @@ -255,16 +275,6 @@ The following command operators are supported:
  * **SI**: Stream idle timeout in addition to 408 response code.
  * **DPE**: The downstream request had an HTTP protocol error.
  -%RESPONSE_TX_DURATION%
  - HTTP
  - Total duration in milliseconds of the request from the first byte read from the upstream host to the last
  - byte sent downstream.
  -
  - TCP
  - Not implemented ("-").
  -
  - Renders a numeric value in typed JSON logs.
  -
  %ROUTE_NAME%
  Name of the route.
  