Make RabbitMQ container fd limit better-suited for demos

1k feels right for a demo environment, where we want to simulate hitting
threshold limits.

deps/rabbitmq_prometheus/docker/docker-compose.yml

@@ -24,6 +24,11 @@ services:
       RABBITMQ_ERLANG_COOKIE: rabbitmq-prometheus
     volumes:
       - ./rabbitmq.conf:/etc/rabbitmq/rabbitmq.conf
+    # we want to simulate hitting thresholds
+    ulimits:
+      nofile:
+        soft: "1024"
+        hard: "2048"
   rabbitmq2:
     << : *rabbitmq
     hostname: rabbitmq2