overrides-exporter exposed default as 0

[tsanghi]

We are currently using cortex-tools to expose Cortex Runtime Config as metrics.

If we defined the following in the runtime config:

overrides:
  tenant1:
    ingestion_burst_size: 10000

The exposed metrics will be:

# HELP cortex_overrides Various different limits.
# TYPE cortex_overrides gauge
cortex_overrides{limit_type="ingestion_burst_size",type="tenant",user="tenant1"} 10000
cortex_overrides{limit_type="ingestion_rate",type="tenant",user="tenant1"} 0

It is wrong for the ingestion_rate since it should be the defaults define in Cortex. It should be:

cortex_overrides{limit_type="ingestion_rate",type="tenant",user="tenant1"} 25000