Add multipath.conf for PX-CSI node driver

PX-CSI requires /etc/multipath.conf to exist on nodes.
Adding Pure Storage FlashArray multipath configuration via Talos machine files.

This fixes node-plugin crash: '/etc/multipath.conf not found'

talos/talhelper/talconfig.yaml

@@ -155,6 +155,36 @@ worker:
           net.ipv4.conf.all.arp_announce: "2"
           net.ipv4.conf.all.arp_ignore: "1"
         
+        # Write multipath.conf for PX-CSI
+        # PX-CSI node driver requires this file to exist
+        files:
+          - content: |
+              defaults {
+                polling_interval 10
+              }
+              devices {
+                device {
+                  vendor "PURE"
+                  product "*"
+                  path_selector "round-robin 0"
+                  path_grouping_policy group_by_prio
+                  prio alua
+                  failback immediate
+                  path_checker tur
+                  fast_io_fail_tmo 10
+                  user_friendly_names no
+                  no_path_retry 0
+                  features "0"
+                  dev_loss_tmo 60
+                }
+              }
+              blacklist {
+                devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
+                devnode "^hd[a-z]"
+              }
+            path: /etc/multipath.conf
+            permissions: 0644
+
 # ─── Nodes ───────────────────────────────────────────────────────────────────
 nodes:
   # ── Control plane ──────────────────────────────────────────────────────────