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/definitions.json

@@ -0,0 +1,26 @@
+{
+    "rabbit_version": "3.13.4",
+    "vhosts": [
+        {
+            "name": "/",
+            "metadata": {
+                "description": "Default virtual host"
+            }
+        }
+    ],
+    "users": [
+        {
+            "name": "xactmon",
+            "tags": []
+        }
+    ],
+    "permissions": [
+        {
+            "user": "xactmon",
+            "vhost": "/",
+            "configure": "^xactmon\\..*",
+            "read": "^xactmon\\..*",
+            "write": "^xactmon\\..*"
+        }
+    ]
+}