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/openssl.cnf

@@ -0,0 +1,17 @@
+[req]
+distinguished_name = root_ca_dn
+prompt = no
+default_md = sha512
+x509_extensions = root_ca
+string_mask = utf8only
+
+[root_ca_dn]
+countryName = US
+organizationName = Dustin C. Hatch
+organizationalUnitName = RabbitMQ
+commonName = RabbitMQ CA
+
+[root_ca]
+subjectKeyIdentifier = hash
+basicConstraints = critical,CA:true,pathlen:0
+keyUsage = cRLSign, keyCertSign