Track reason why a query result is not cached

[pracucci]

We should add a metric to track the reason why a query results is not cached, and ensure we have another metric with the total number of queries for which we've the check to compare with.

https://github.com/grafana/mimir/blob/321e66db90cf39e8eb1067aada9064d15cac4ba9/pkg/frontend/querymiddleware/results_cache.go#L176-L194

Originally posted by @pracucci in https://github.com/grafana/mimir/issues/1744#issuecomment-1185265393

[pracucci]

We should also display it in the "Mimir / Queries" dashboard.