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/ca/rabbitmq-ca.yaml

@@ -0,0 +1,7 @@
+apiVersion: cert-manager.io/v1
+kind: ClusterIssuer
+metadata:
+  name: rabbitmq-ca
+spec:
+  ca:
+    secretName: rabbitmq-ca