add queue/kafka plugin

[benjamonnguyen]

Fixes #

Changes proposed in this pull request:

• add queue/kafka plugin

Checklist:

• docs updated
• tests updated
• Changes updated

[msimerson]

Thank you for this submission. As a general rule, we no longer bundle plug-ins with Haraka and instead package them as independent NPM modules. I have been slowly unbundling plugins. This is especially true for plugins that add dependencies.

I'd suggest releasing this as haraka-plugin-queue-kafka. There is a plugin template that helps bootstrap the process.