Monitoring - Fixed influxdb write on sentMessageStats

[uro]

I deep dive into one bug on monitoring package, I found that message statistics are not accepted by influxdb (even by 1 year old revision), we always receive message

{"error":"unable to parse 'sent-messages,destination=example_topic,command=example_command 1546449295702': invalid field format"}

Which means that it's not passing influxdb requirements - LINK. I checked it and yes, we can send empty value, but only if we have some additional fields. In our case we don't have any fields and no value (which is field as well).

Steps to reproduce:

1. Try to send request to influxdb with current state:
   curl -i -XPOST 'http://localhost:8086/write?db=mydb' --data-binary 'sent-messages,destination=example_topic,command=example_command 1546449295702'
   code: 400, response: {"error":"unable to parse 'sent-messages,destination=example_topic,command=example_command 1546449295702': invalid field format"}

2. Try to add field, for example value:
   curl -i -XPOST 'http://localhost:8086/write?db=mydb' --data-binary 'sent-messages,destination=example_topic,command=example_command value=1 1546449295702'
   code: 204, no content 👍

Instead of value we can send something else, but we have to send something.

Could you help with this @ASKozienko?

[uro]

Additionally message from consoleLogger:

10:14:48 ERROR     [app] [ClientMonitoringExtension] Push to storage failed: HTTP Code 400 {"error":"unable to parse 'sent-messages,destination=my_queue,topic=my_topic  1546510487996': invalid field format"}

[makasim]

@uro is this fix working for you? Is there something you want to add or it is ready to be merged?

[uro]

@makasim Yes it works now 👍

The problem is that we need to have some "fields". I put value=1 as the simplest solution which is not changing anything.
Technically I can replace it with any of these https://github.com/php-enqueue/enqueue-dev/blob/master/pkg/monitoring/SentMessageStats.php attributes or add more. As I don't need them I didn't do any changes which are not required.

If you like me to add them (to make it better) I can do that, otherwise it's ready for merge

[makasim]

thanks @uro