WPB-5069 Docs for rabbitmq-consumer

changelog.d/5-internal/WPB-4748

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-CLI tool to consume messages from a RabbitMQ queue
+CLI tool to consume messages from a RabbitMQ queue (#3589, #3655)

docs/src/developer/reference/rabbitmq-consumer.md

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+# RabbitMQ Consumer
+
+`rabbitmq-consumer` can be used to inspect and drop blocking messages from a RabbitMQ queue containing outgoing messages to another backend.
+
+E.g. in the following screen shot of the RabbitMQ management UI you can see that a message is stuck in the `backend-notifications.d1.example.com` queue:
+
+![rabbitmqadmin](rabbitmq-consumer/rabbitmqadmin.png)
+
+## Interactively inspect/drop messages
+
+Follow these steps to inspect (and/or drop) the message:
+
+1. Stop the background-worker because the queues are single active consumer queues. One way to do this is to set the background-worker's `replicas` count to 0 in the k8s deployment. The number of unacked messages should then switch to 0.
+
+2. Run:
+
+```shell
+RABBITMQ_HOST=<host> # default: "localhost"
+RABBITMQ_PORT=<port> # default: 5672
+RABBITMQ_USER=<user>
+RABBITMQ_PW=<password>
+RABBITMQ_VHOST=<vhost> # default: "/"
+RABBITMQ_QUEUE=<queue>
+WIRE_VERSION=<version>
+
+docker run -it --network=host "quay.io/wire/rabbitmq-consumer:$WIRE_VERSION" \
+  --host "$RABBITMQ_HOST" \
+  --port "$RABBITMQ_PORT" \
+  --username "$RABBITMQ_USER" \
+  --password "$RABBITMQ_PW" \
+  --vhost "$RABBITMQ_VHOST" \
+  --queue "$RABBITMQ_QUEUE" \
+  interactive
+```
+
+The output will look similar to:
+
+```
+vhost: backendA
+queue: backend-notifications.d1.example.com
+timestamp: Nothing
+received message:
+{
+    "body": {
+        "conversation": "7d86646e-1122-4979-8629-22dbd6e22afe",
+        "data": "",
+        "priority": null,
+        "push": true,
+        "recipients": {
+            "d0c931d3-ee12-43e5-8c97-26f5b9b1ee6d": {
+                "ea035ddd6d9647d5": "c3VjY2VzcyBtZXNzYWdlIGZvciBkb3duIHVzZXI="
+            }
+        },
+        "sender": {
+            "domain": "example.com",
+            "id": "83c78b82-545d-4f29-aec4-ae29ea5231d0"
+        },
+        "sender_client": "550d8c614fd20299",
+        "time": "2023-10-17T10:39:46.38476388Z",
+        "transient": false
+    },
+    "ownDomain": "example.com",
+    "path": "/on-message-sent",
+    "targetComponent": "galley"
+}
+type 'drop' to drop the message and terminate, or press enter to terminate without dropping the message
+```
+
+Now the message can be dropped by typing: `drop`.
+
+## Non-interactive commands
+
+There are 2 non-interactive commands:
+
+- `head`: prints the first message in the queue
+- `drop-head (-a|--path PATH)`: drops the first message from the queue if the provided path argument matches the path field of the message
+
+These commands will time out (after 10 seconds per default) if no messages are received within this time.
+This can happen when the queue is empty, or when we lose the single active consumer race.
+
+## Help
+
+```shell
+WIRE_VERSION=<version>
+
+docker run -it --network=host "quay.io/wire/rabbitmq-consumer:$WIRE_VERSION" --help
+```
+
+```
+rabbitmq-consumer
+
+Usage: rabbitmq-consumer [-s|--host HOST] [-p|--port PORT]
+                         [-u|--username USERNAME] [-w|--password PASSWORD]
+                         [-v|--vhost VHOST] [-q|--queue QUEUE]
+                         [-t|--timeout TIMEOUT] COMMAND
+
+  CLI tool to consume messages from a RabbitMQ queue
+
+Available options:
+  -h,--help                Show this help text
+  -s,--host HOST           RabbitMQ host (default: "localhost")
+  -p,--port PORT           RabbitMQ Port (default: 5672)
+  -u,--username USERNAME   RabbitMQ Username (default: "guest")
+  -w,--password PASSWORD   RabbitMQ Password (default: "alpaca-grapefruit")
+  -v,--vhost VHOST         RabbitMQ VHost (default: "/")
+  -q,--queue QUEUE         RabbitMQ Queue (default: "test")
+  -t,--timeout TIMEOUT     Timeout in seconds. The command will timeout if no
+                           messages are received within this time. This can
+                           happen when the queue is empty, or when we lose the
+                           single active consumer race. (default: 10)
+
+Available commands:
+  head                     Print the first message in the queue
+  drop-head                Drop the first message in the queue
+  interactive              Interactively drop the first message from the queue
+```