Add missing strings for errors in amberelectric config flow (#78140)

homeassistant/components/amberelectric/strings.json

@@ -15,6 +15,11 @@
         },
         "description": "Select the NMI of the site you would like to add"
       }
+    },
+    "error": {
+      "invalid_api_token": "[%key:common::config_flow::error::invalid_api_key%]",
+      "no_site": "No site provided",
+      "unknown_error": "[%key:common::config_flow::error::unknown%]"
     }
   }
 }

homeassistant/components/amberelectric/translations/en.json

@@ -15,6 +15,11 @@
                 },
                 "description": "Go to {api_url} to generate an API key"
             }
+        },
+        "error": {
+          "invalid_api_token": "Invalid API key",
+          "no_site": "No site provided",
+          "unknown_error": "Unexpected error"
         }
     }
 }