Option to disable systemd syslog in docker::run + Document extra_systemd_parameters

Use Case

A normal docker setup do not syslog container output to the systemd journal (by default container output is placed in json logfiles under /var/lib/docker/containers/*/*.log).
Only internal messages from the docker daemon itself are syslogged, not the container output.

However, the puppetlabs docker module builds a systemd service file for each continer to run, and by default, systemd syslogs all stdout and stderr for all services.
So suddently a system get double logs. First the direct json-logs in /var/lib/docker/containers/*/*.log and then the same thing is spammed to the journal, and therefore also spammed to /var/log/* (if the system is running a syslog service).

Describe the Solution You Would Like

I want an option to stop the docker::run systemd service syslogging, and only log whatever I have configured in docker, globally or in container specific options.

In docker::run you already have the options syslog_identifier and syslog_facility to tweak the syslog from the systemd service.
I would like this new extra option:
syslog_enable = true/false (default should be true, because this module has always worked this (incorrect) way)

When set to false, the /etc/systemd/system/docker-containername.service unit should get these two extra lines:

[Service]
StandardOutput=null
StandardError=null

This will mute all output from the container-service, and we're back to a "normal" setup.

Describe Alternatives You've Considered

I see there is an option extra_systemd_parameters, but it is totally undocumented.
Can/should it be used to solve the above?

In the meantime I've created this workaround:
In the profile where I docker::run my container, I've added this systemd dropin-file:

  file { '/etc/systemd/system/docker-foobar.service.d':
    ensure  => directory,
  }
  file { '/etc/systemd/system/docker-foobar.service.d/mute_output.conf':
    content => "### Managed by puppet ###\n[Service]\nStandardOutput=null\nStandardError=null\n",
    require => File['/etc/systemd/system/docker-foobar.service.d'],
  }

Oh, in any case, please document the extra_systemd_parameters option and give an example how to use it.

Start at the docker::run systemd unit generation and the existing extra_systemd_parameters entry point. Confirm how syslog_identifier and syslog_facility are handled, then add the requested option and document extra_systemd_parameters with an example; done means the generated unit can disable stdout and stderr logging and the option is documented.