Adding "distributor" section support to mimir config file

[HamzaKhait]

Hello,

This small edit allows users to add distributor section to mimir config file. The distributor section is mandatory for Mimir high-availability deduplication. Here's an example :

... 

limits:
  accept_ha_samples: true


distributor:
  ha_tracker:
    enable_ha_tracker: true
    kvstore:
      store: etcd
      etcd:
        tls_enabled: false
        endpoints:
        - 10.103.0.174:2379
        - 10.103.0.71:2379