grafana: auto add label filter for metrics

[skyzh]

For all metrics like:

histogram_quantile(0.9, sum(rate(object_store_operation_bytes_bucket[1m])) by (le, type))

We should support automatically rewrite them into

histogram_quantile(0.9, sum(rate(object_store_operation_bytes_bucket{ job = "$job", instance = "$instance" }[1m])) by (le, type))

So that users can filter easily by instance or by job.