Feature/helm single binary extra containers (#8956)

**What this PR does / why we need it**:
Add a new helm value `singleBinary.extraContainers` to allow running
sidecar containers in a singleBinary loki deployment. Useful for a
container that keeps the data PV from filling up.

**Checklist**
- [ ] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

docs/sources/installation/helm/reference.md

@@ -3061,6 +3061,15 @@ null
 			<td><pre lang="json">
 []
 </pre>
+</td>
+		</tr>
+		<tr>
+			<td>singleBinary.extraContainers</td>
+			<td>list</td>
+			<td>Extra containers to add to the single binary loki pod</td>
+			<td><pre lang="json">
+[]
+</pre>
 </td>
 		</tr>
 		<tr>

production/helm/loki/templates/single-binary/statefulset.yaml

@@ -120,6 +120,9 @@ spec:
             {{- end }}
           resources:
             {{- toYaml .Values.singleBinary.resources | nindent 12 }}
+        {{- with .Values.singleBinary.extraContainers }}
+        {{- toYaml . | nindent 8 }}
+        {{- end }}
       {{- with .Values.singleBinary.affinity }}
       affinity:
         {{- tpl . $ | nindent 8 }}

production/helm/loki/values.yaml

@@ -909,6 +909,8 @@ singleBinary:
   extraEnv: []
   # -- Environment variables from secrets or configmaps to add to the single binary pods
   extraEnvFrom: []
+  # -- Extra containers to add to the single binary loki pod
+  extraContainers: []
   # -- Init containers to add to the single binary pods
   initContainers: []
   # -- Volume mounts to add to the single binary pods