fix grafana helm values to match chart 7.x template expectations
- extraContainerVolumeMounts doesn't exist in this chart; use
extraVolumeMounts (list, iterated with range)
- extraContainers is templated with tpl (expects string), not toYaml
(list) — use YAML literal block scalar
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>