chore: follow-up to grafana#11151 and grafana#11025 (grafana#11225)

**What this PR does / why we need it**:

- remove usage of `enforce_metric_name` in ksonnet -
grafana#11151
- make `cortex_ruler_client_request_duration_seconds` prefix
configurable
- updates upgrade guide to remove reference to metrics that loki does
not export

**Which issue(s) this PR fixes**:
Fixes #<issue number>

**Special notes for your reviewer**:

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] If the change is worth mentioning in the release notes, add
`add-to-release-notes` label
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/setup/upgrade/_index.md`
- [ ] For Helm chart changes bump the Helm chart version in
`production/helm/loki/Chart.yaml` and update
`production/helm/loki/CHANGELOG.md` and
`production/helm/loki/README.md`. [Example
PR](grafana@2cef71e)
- [ ] If the change is deprecating or removing a configuration option,
update the `deprecated-config.yaml` and `deleted-config.yaml` files
respectively in the `tools/deprecated-config-checker` directory.
[Example
PR](grafana@0d4416a)

production/helm/loki/values.yaml

@@ -254,7 +254,6 @@ loki:
     grpc_listen_port: 9095
   # -- Limits config
   limits_config:
-    enforce_metric_name: false
     reject_old_samples: true
     reject_old_samples_max_age: 168h
     max_cache_freshness_per_query: 10m