Add local service object (#10907)

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

Otherwise the jsonnet is invalid

**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](d10549e)

Signed-off-by: Michel Hollands <[email protected]>

production/ksonnet/loki/index-gateway.libsonnet

@@ -71,6 +71,7 @@
   else {},
 
   index_gateway_headless_service: if $._config.use_index_gateway then
+    local service = k.core.v1.service;
     k.util.serviceFor($.index_gateway_statefulset, $._config.service_ignored_labels) +
     service.mixin.metadata.withName('index-gateway-headless') +
     service.mixin.spec.withClusterIp('None')