add prometheus_rabbitmq_exporter

[nlopez]

This adds the prometheus_rabbitmq_exporter RabbitMQ plugin described here to the RabbitMQ image.

This doesn't enable the plugin by default. To do so, AWX cluster operators will need to add prometheus_rabbitmq_exporter to their enabled_plugins config, around here.

I moved launch.sh along with my fetch script for the RabbitMQ modules to a rootfs dir to avoid cluttering the repo root, but I can back this out if you don't want to use this pattern.

[wenottingham]

Just to state the obvious question: why?

[nlopez]

Why include the prom exporter or why the rootfs dir?

Prom exporter: Because I'm running into some queue pileup issues with AWX and want to monitor the AWX RabbitMQ cluster via Prometheus, and figure other AWX users may want to do the same.

[wenottingham]

Sure, I just wonder whether if we did this we should also have AWX itself throwing metrics into prometheus.

[nlopez]

Oh definitely! In fact I'm still hoping to be able to contribute something towards ansible/awx#1963 in the future.

I think this'd still be useful to have at any rate for people wanting to do per component monitoring, similar to how you'd monitor the AWX Postgres DB.