Update Matter boost duration description to specify units in seconds (home-assistant#155185)

Author: lboue

homeassistant/components/matter/strings.json

@@ -600,7 +600,7 @@
       "fields": {
         "duration": {
           "name": "Duration",
-          "description": "Boost duration"
+          "description": "Boost duration in seconds."
         },
         "emergency_boost": {
           "name": "Emergency boost",