Chunk mixin is not deployed by default

[cyriltovena]

I created a new env with this:

  mixins+:: cortex_grafana_mixins {
    loki: loki_mixin,
    billing: billing_mixin,
  },

Turns out this is not enough to deploy a default configuration, I was expecting chunks mixin to be deployed. However this worked:

  mixins+:: cortex_grafana_mixins {
    loki: loki_mixin,
    billing: billing_mixin,
    cortex+: {
      _config+:: {
        storage_engine: ['chunks'], 
      },
    },
  },

I think by default we should deploy chunks mixin.

[pracucci]

I assumed it would have used these defaults: https://github.com/grafana/cortex-jsonnet/blob/56cb5e3d73950b977ba2e4bfd7e46e2acb0b77b2/cortex-mixin/config.libsonnet#L5-L9

But I guess there's an issue somewhere.