[AETHER-3071] Export num configured and reachable devices to Prometheus

Change-Id: I8cf178e6596460433f3b82c85e3d311e6f96f032
diff --git a/requirements.txt b/requirements.txt
index c51d4df..06b8f1c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,6 +10,7 @@
 itsdangerous==2.0.1
 Jinja2==3.0.3
 MarkupSafe==2.0.1
+prometheus-client==0.13.1
 pyaml==21.10.1
 pytz==2021.3
 PyYAML==6.0