Add the scan speed option for service discovery

bamboo/translations/en.yaml

@@ -14,3 +14,6 @@ configuration:
   discover_ports:
     name: Scan ports
     description: "The TCP ports to try when scanning, for example 22,80,443,8000-8010. Leave empty for a short list of common ones."
+  discover_rate:
+    name: Scan speed
+    description: The most connection attempts per second a scan may make. The default is 50.