Stop using deprecated panel type graph in mimir-mixin

[krajorama]

Describe the bug

Mimir mixin is using a deprecated Grafana UI panel type, causing the frontend to convert the dashboards all the time (or make user save it causing it to be out of sync with the source).

To Reproduce

See e.g. https://github.com/grafana/mimir/blob/main/operations/mimir-mixin-compiled/dashboards/mimir-writes.json#L508

Expected behavior

Dashboards should use "timeseries" panel type instead but look the same.

Environment

Any.

Additional Context

The dashboards are generated from jsonnet in https://github.com/grafana/mimir/tree/main/operations/mimir-mixin using https://github.com/grafana/jsonnet-libs/tree/master/grafana-builder

[krajorama]

Some work has been done on this already:
#2800
#6864
probably more

[jmichalek132]

I would be willing to help with this one.

[narqo]

@jmichalek132 I'm working on that in #7413. If you could help with testing the changes, to possibly spot any unexpected discrepancies in the dashboards before/after, this would be very helpful.