disable imklog for containers

By default rsyslog has imklog module enabled in /etc/rsyslog.conf

# provides kernel logging support and enable non-kernel klog messages
module(load="imklog" permitnonkernelfacility="on")

This module reads from /proc/kmsg which requires root privilege.

However, when running rsyslog in a (LXD, Docker) container, the container doesn't often have root privilege.
This results in having a lot of error messages in rsyslog's output.

Mar 6 01:00:33 juju-ba8709-8-lxd-16 rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Permission denied.
Mar 6 01:01:56 juju-ba8709-8-lxd-16 rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Permission denied.
Mar 6 01:13:41 juju-ba8709-8-lxd-16 rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Permission denied.
Mar 6 01:14:10 juju-ba8709-8-lxd-16 rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Permission denied.
Mar 6 04:40:49 juju-ba8709-8-lxd-16 rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Permission denied.

Currently the user has to use another tool, such as ansible or puppet to disable this module in /etc/rsyslog.conf.
It would be good if this charm can do that too.