chore(deps): update sourcegraph prometheus / grafana docker images to v6.12.0

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:6.12.0@sha256:af7d4977efec2a814ea43c6d49f623ced2054b2436dba5abb30af8b1c3a3ca06'
     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:6.12.0@sha256:16b11b33872819757fd34eb72fd957b2fbb362c9a87a1c43fb7ab8666b1c0770'
     cpus: 1
     mem_limit: '1g'
     volumes: