Update dependency prometheus_client to v0.9.0

Author: renovate-bot

requirements.txt

@@ -4,7 +4,7 @@ influxdb
 msgpack>=0.4.6,<1.0.0
 networkx
 pbr>=1.9
-prometheus_client==0.8.0
+prometheus_client==0.9.0
 pyyaml==5.3.1
 ryu==4.32
 beka==0.3.4