Add secondary-info: last-triggered (#4222)

* Add secondary-info: last-triggered

add last-triggered to the currently available options 'entity-id' and 'last-changed' see:https://www.home-assistant.io/lovelace/entities/#secondary_info

* corrected omission 'attributes'

* added test for attributes.last_triggered

* Update hui-generic-entity-row.ts

* Update hui-generic-entity-row.ts

src/panels/lovelace/components/hui-generic-entity-row.ts

@@ -105,6 +105,14 @@ class HuiGenericEntityRow extends LitElement {
                     .datetime=${stateObj.last_changed}
                   ></ha-relative-time>
                 `
+              : this.config.secondary_info === "last-triggered" &&
+                stateObj.attributes.last_triggered
+              ? html`
+                  <ha-relative-time
+                    .hass=${this.hass}
+                    .datetime=${stateObj.attributes.last_triggered}
+                  ></ha-relative-time>
+                `
               : ""}
           </div>
         </div>