rabbitmq: Deploy RabbitMQ Server

RabbitMQ is an AMQP message broker.  It will be used by `xactmon` to
pass messages between the components.

Although RabbitMQ can be deployed in a high-availability cluster, we
don't really need that level of robustness for `xactmon`, so we will
just run a single instance.  Deploying a single-host RabbitMQ server
is pretty straightforward.

We're using mTLS authentication; clients need to have a certificate
issued by the *RabbitMQ CA* in order to connect to the message broker.
The `rabbitmq-ca` _cert-manager_ ClusterIssuer issues these certificates
for in-cluster services like `xactmon`.

rabbitmq/namespace.yaml

@@ -0,0 +1,7 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: rabbitmq
+  labels:
+    app.kubernetes.io/component: rabbitmq
+    app.kubernetes.io/name: rabbitmq