rsyslog - how to send multipline messages using JSON template - rsyslog

Question

I am shipping laravel logs using the rsyslog imfile module.
I use the startmsg.regex to deal with multiline messages. These work great.
input(type="imfile"
File="laravel.log"
Tag="laravel_app"
startmsg.regex="[[:digit:]]{4}-[[:digit:]]{1,2}-[[:digit:]]{1,2} [[:digit:]]{1,2}:[[:digit:]]{1,2}:[[:digit:]]{1,2}"
)
I then ship the logs out to Logstash (and then use them in Elasticsearch, and Kibana)
I ship the logs using a Rsyslog template
template(name="json-template"
type="list") {
constant(value="{")
constant(value="\"#timestamp\":\"") property(name="timereported" dateFormat="rfc3339")
constant(value="\",\"#version\":\"1")
constant(value="\",\"message\":\"") property(name="msg" format="json")
constant(value="\",\"sysloghost\":\"") property(name="hostname")
constant(value="\",\"severity\":\"") property(name="syslogseverity-text")
constant(value="\",\"facility\":\"") property(name="syslogfacility-text")
constant(value="\",\"programname\":\"") property(name="programname")
constant(value="\",\"procid\":\"") property(name="procid")
constant(value="\"}\n")
}
My logs look like this, where line-breaks are marked with \n
[2018-06-07 11:02:33] testing.ERROR: Class 'App\Http\Controllers\Deal'
not found {"exception":"[object]
(Symfony\Component\Debug\Exception\FatalThrowableError(code: 0): Class
'App\Http\Controllers\Deal' not found at
/app/Http/Controllers/TestingSyslogController.php:13)\n[stacktrace]\n#0
[internal function]:
App\Http\Controllers\TestingSyslogController->index()\n#1
/vendor/laravel/framework/src/Illuminate/Routing/Controller.php(54):
call_user_func_array(Array, Array)\n#2
/vendor/laravel/framework/src/Illuminate/Routing/ControllerDispatcher.php(45):
Illuminate\Routing\Controller->callAction('index', Array)\n#3
/vendor/laravel/framework/src/Illuminate/Routing/Route.php(212):
Illuminate\Routing\ControllerDispatcher->dispatch(Object(Illuminate\Routing\Route),
Object(App\Http\Controllers\TestingSyslogController), 'index')\n#4
/vendor/laravel/framework/src/Illuminate/Routing/Route.php(169):
Illuminate\Routing\Route->runController()\n#5
So the entire message is in a single line {message}
How can I use the rsyslog template to split the message at '\n' into different objects to look something like this...
{message line 1},{message line 2},{message line x}