fix(helm): update chart grafana to 6.58.8

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
grafana (source)	patch	6.58.7 -> 6.58.8

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Release Notes

grafana/helm-charts (grafana)

### [`v6.58.8`](https://togithub.com/grafana/helm-charts/releases/tag/grafana-6.58.8) [Compare Source](https://togithub.com/grafana/helm-charts/compare/grafana-6.58.7...grafana-6.58.8) The leading tool for querying and visualizing time series and metrics. #### What's Changed - \[grafana] allow configuring serviceMonitor.metricRelabelings by [@​clux](https://togithub.com/clux) in [https://github.com/grafana/helm-charts/pull/2580](https://togithub.com/grafana/helm-charts/pull/2580) #### New Contributors - [@​clux](https://togithub.com/clux) made their first contribution in [https://github.com/grafana/helm-charts/pull/2580](https://togithub.com/grafana/helm-charts/pull/2580) **Full Changelog**: https://github.com/grafana/helm-charts/compare/promtail-6.14.2...grafana-6.58.8

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