Add relative timestamp state_content for input_datetime (#24135)

* Fix digit grouping in input_datetime `year`

* Display `input_datetime`s `timestamp` attribute as relative time instead of number

src/data/entity_attributes.ts

@@ -115,6 +115,9 @@ export const DOMAIN_ATTRIBUTES_FORMATERS: Record<
       return formatDurationDigital(locale, { hours, minutes, seconds })!;
     },
   },
+  input_datetime: {
+    year: (value) => value.toString(),
+  },
 };
 
 export const NON_NUMERIC_ATTRIBUTES = [

src/state-display/state-display.ts

@@ -104,7 +104,7 @@ class StateDisplay extends LitElement {
       return html`${this.name || computeStateName(stateObj)}`;
     }
 
-    let relativeDateTime: string | undefined;
+    let relativeDateTime: string | Date | undefined;
 
     // Check last-changed for backwards compatibility
     if (content === "last_changed" || content === "last-changed") {
@@ -114,6 +114,9 @@ class StateDisplay extends LitElement {
     if (content === "last_updated" || content === "last-updated") {
       relativeDateTime = stateObj.last_updated;
     }
+    if (domain === "input_datetime" && content === "timestamp") {
+      relativeDateTime = new Date(stateObj.attributes.timestamp * 1000);
+    }
 
     if (
       content === "last_triggered" ||