feat: Helm: Add extraContainers to backend pods (#16205)

**What this PR does / why we need it**:
This PR adds the `extraContainers` property to the backend Loki pods for the Loki helm chart.

**Which issue(s) this PR fixes**:
Fixes #16164

Author: mgbz89

docs/sources/setup/install/helm/reference.md

@@ -324,6 +324,7 @@ This is the generated reference for the Loki Helm Chart values.
   },
   "dnsConfig": {},
   "extraArgs": [],
+  "extraContainers": [],
   "extraEnv": [],
   "extraEnvFrom": [],
   "extraVolumeMounts": [],
@@ -453,6 +454,15 @@ null
 			<td><pre lang="json">
 []
 </pre>
+</td>
+		</tr>
+		<tr>
+			<td>backend.extraContainers</td>
+			<td>list</td>
+			<td>Containers to add to the backend pods</td>
+			<td><pre lang="json">
+[]
+</pre>
 </td>
 		</tr>
 		<tr>

production/helm/loki/CHANGELOG.md

@@ -13,6 +13,8 @@ Entries should include a reference to the pull request that introduced the chang
 
 [//]: # (<AUTOMATED_UPDATES_LOCATOR> : do not remove this line. This locator is used by the CI pipeline to automatically create a changelog entry for each new Loki release. Add other chart versions and respective changelog entries bellow this line.)
 
+- [CHANGE] Add extraContainers parameter for the backend pod
+
 ## 6.27.0
 
 - [FEATURE] Added support for globals: `extraArgs`, `extraEnv`, `extraEnvFrom`, `extraVolumes`, `extraVolumeMounts` ([#16062](https://github.com/grafana/loki/pull/16062)) relates to ([#12652](https://github.com/grafana/loki/pull/12652))

production/helm/loki/templates/backend/statefulset-backend.yaml

@@ -198,6 +198,9 @@ spec:
             {{- end }}
           resources:
             {{- toYaml .Values.backend.resources | nindent 12 }}
+        {{- with .Values.backend.extraContainers }}
+        {{- toYaml . | nindent 8}}
+        {{- end }}
       {{- with .Values.backend.affinity }}
       affinity:
         {{- toYaml . | nindent 8 }}

production/helm/loki/values.yaml

@@ -1735,6 +1735,8 @@ backend:
   extraEnvFrom: []
   # -- Init containers to add to the backend pods
   initContainers: []
+  # -- Containers to add to the backend pods
+  extraContainers: []
   # -- Volume mounts to add to the backend pods
   extraVolumeMounts: []
   # -- Volumes to add to the backend pods