feat: add init container to install Mattermost Calls plugin

k8s/nextgen/20-mattermost.yaml

@@ -81,6 +81,26 @@ spec:
       labels:
         app: mattermost
     spec:
+      initContainers:
+        - name: install-calls-plugin
+          image: alpine
+          command:
+            - sh
+            - -c
+            - |
+              apk add --no-cache ca-certificates wget tar
+              if [ ! -d /mattermost/plugins/com.mattermost.calls ]; then
+                echo "Downloading Mattermost Calls plugin..."
+                wget -qO calls.tar.gz https://github.com/mattermost/mattermost-plugin-calls/releases/latest/download/com.mattermost.calls-linux-amd64.tar.gz
+                tar -xzf calls.tar.gz -C /mattermost/plugins/
+                rm calls.tar.gz
+                echo "Mattermost Calls plugin installed."
+              else
+                echo "Mattermost Calls plugin already installed."
+              fi
+          volumeMounts:
+            - name: mattermost-plugins
+              mountPath: /mattermost/plugins
       containers:
         - name: mattermost
           image: mattermost/mattermost-team-edition:9.11