message: docs: document the the allow-unknown-fields cli flag
diff: @@ -235,3 +235,10 @@ following are the command line options that Envoy supports.
  *(optional)* This flag disables Envoy hot restart for builds that have it enabled. By default, hot
  restart is enabled.
  +
  +.. option:: --allow-unknown-fields
  +
  + *(optional)* This flag disables validation of protobuf configurations for unknown fields. By default, the
  + validation is enabled. For most deployments, the default should be used which ensures configuration errors
  + are caught upfront and Envoy is configured as intended. However in cases where Envoy needs to accept configuration
  + produced by newer control planes, effectively ignoring new features it does not know about yet, this can be disabled.
  