chore(deps): update sourcegraph prometheus / grafana docker images to v6.9.0

Author: renovate[bot]

docker-compose/docker-compose.yaml

@@ -419,7 +419,7 @@ services:
   #
   prometheus:
     container_name: prometheus
-    image: 'index.docker.io/sourcegraph/prometheus:6.1.2889@sha256:75fa45933ecb03f7aca1d54ec5ebc05d11ff300494a2ca8fbaefa25c83f0326f'
+    image: 'index.docker.io/sourcegraph/prometheus:6.9.0@sha256:f9b456110b2755214ec6767196f4971742f22c4f9fbe25326328f11041a4fc5d'
     cpus: 4
     mem_limit: '8g'
     volumes:
@@ -446,7 +446,7 @@ services:
   # 'GF_SERVER_ROOT_URL='https://grafana.example.com'
   grafana:
     container_name: grafana
-    image: 'index.docker.io/sourcegraph/grafana:6.3.3@sha256:2f68b9b1542e7d75459d983b606d2fdd1c11a75610464e3d7a6ced4f3ac474bf'
+    image: 'index.docker.io/sourcegraph/grafana:6.9.0@sha256:52e1a6b845ccb1584f56bcbc6c517eedbec0d955aad64ee9a8ce3c5859a07b4b'
     cpus: 1
     mem_limit: '1g'
     volumes: