DLQ support

[morel666]

This is rather request for feature not issue - It would be very useful if this plugin will support Logstash DLQ. Do you plan to add such mechanism?

[theangryangel]

It's on my list of things to look at, but I've not gotten around to it yet :) Last I looked it wasn't released.

As always, PRs are always welcome.

[theangryangel]

I've had a very quick look before work this morning, it looks pretty straight forward to implement.

The only thing that needs some thought is how to integrate it with the existing retry mechanisms (which uses SQL state codes). If I get some time this week I'll look at implementing something and then getting your feedback.

[theangryangel]

https://github.com/theangryangel/logstash-output-jdbc/tree/feat/dlq_support starts adding support. I've untested, but hopefully I'll find a moment to finish an initial implementation and tests later this week.