Cortex kv panel improvements

[bboreham]

What this PR does:

Distributor uses multiple kv stores - for global limits and ha-tracker, as well as reading from the ingester ring - so we need to narrow the panel to just the one it says it is showing, e.g. kv_name="distributor-hatracker".

For consistency, do the same on the ingester panel, although currently ingesters only have one kv store.

Created as Draft because the renamed recording rule will mean that dashboards show no data for latency prior to the change. Do we want to cope with this? We could add an extra three queries on the latency panels with the old name, but it will get quite ugly in the code. Discuss.

Also, I added a couple of panels with more info on what the KV store is doing.

• For HA-tracker, show which tenants are changing election.
• For ingester, show how many are active, leaving, etc.

Checklist

• [x] CHANGELOG.md updated

[CLAassistant]

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