Merge branch 'jv-praefect-disable-grafana' into 'master'

Disable grafana on Gitaly/Praefect backend nodes

Closes gitaly#2256

See merge request gitlab-org/gitlab!21766

doc/administration/gitaly/praefect.md

@@ -79,6 +79,7 @@ postgresql['enable'] = false
 redis['enable'] = false
 nginx['enable'] = false
 prometheus['enable'] = false
+grafana['enable'] = false
 unicorn['enable'] = false
 sidekiq['enable'] = false
 gitlab_workhorse['enable'] = false
@@ -150,6 +151,7 @@ postgresql['enable'] = false
 redis['enable'] = false
 nginx['enable'] = false
 prometheus['enable'] = false
+grafana['enable'] = false
 unicorn['enable'] = false
 sidekiq['enable'] = false
 gitlab_workhorse['enable'] = false