Fix iscsi-multipath-init DaemonSet for Talos read-only filesystem

Use nsenter to write multipath.conf in host's mount namespace instead
of trying to write to /host/etc which is read-only in containers.

Talos mounts /etc as read-only in container namespaces but allows writes
in the host mount namespace. This fix uses nsenter to access PID 1's
mount namespace where /etc is writable.

Also removed unnecessary volumeMounts and volumes since we're using
nsenter instead of hostPath mounts.

Fixes: Init:Error - 'can't create /host/etc/multipath.conf: Read-only file system'

talos/talhelper/iscsi-multipath-init.yaml

@@ -51,8 +51,9 @@ spec:
           
           echo "Configuring multipath for Pure Storage FlashArray..."
           
-          # Write multipath.conf
-          cat > /host/etc/multipath.conf <<'MPCONF'
+          # Write multipath.conf using nsenter to access host's writable filesystem
+          # Talos mounts /etc as read-only in containers, but writable in host namespace
+          nsenter -t 1 -m -u -i -n -- sh -c 'cat > /etc/multipath.conf' <<'MPCONF'
           # Multipath configuration for Pure Storage FlashArray
           # Managed by iscsi-multipath-init DaemonSet
           
@@ -97,10 +98,6 @@ spec:
           echo "✓ Multipath configuration complete"
           echo "Current multipath devices:"
           nsenter -t 1 -m -u -i -n -- multipath -ll || echo "  (no multipath devices yet)"
-          
-        volumeMounts:
-        - name: host-etc
-          mountPath: /host/etc
       
       containers:
       # Pause container keeps the pod running to indicate configuration is applied
@@ -113,9 +110,3 @@ spec:
           limits:
             cpu: 10m
             memory: 16Mi
-      
-      volumes:
-      - name: host-etc
-        hostPath:
-          path: /etc
-          type: Directory