[loki-distributed] Add cluster_label default to prevent cross-talk from other memberlists.

[Aaron-ML]

Is your feature request related to a problem? Please describe.
Looks like #6658 got merged, which is awesome. I see no harm in defaulting this into the chart as a default safe option.

Describe the solution you'd like
defaulting a memberlist config like:

memberlist:
  cluster_label: {{ loki.fullname }}
  cluster_label_verification_disabled: false
  join_members:
  - {{ loki.fullname }}

Describe alternatives you've considered
Right now we are defaulting this with structureConfig overrides. It works but others will run into this problem if they deploy similar services without adding it leading to additional confusion and problematic installs. For instance if tempo and loki run on the same cluster. I'll work on this as a PR from this issue if I get the time. Thanks

[trevorwhitney]

hey @Aaron-ML just to double check based on the title, you're suggesting this for the helm chart at production/helm/loki (which is published as grafana/loki), and not looking to make a change to grafana/loki-distributed (which lives in the grafana/helm-charts repo) correct?