Expose the "start-background-broker" CMD

BUILD.bazel

@@ -165,6 +165,14 @@ rabbitmq_run_command(
     subcommand = "run-broker",
 )
 
+# Allow us to `bazel run background-broker`
+# to start a broker in the background
+rabbitmq_run_command(
+    name = "background-broker",
+    rabbitmq_run = ":rabbitmq-run",
+    subcommand = "start-background-broker",
+)
+
 # Allow us to `bazel run start-cluster`
 # for the equivalent of `make start-cluster`
 rabbitmq_run_command(