Added relative timestamps to feed objects

ref https://linear.app/tryghost/issue/AP-131/show-nice-relative-timestamps

apps/admin-x-activitypub/src/utils/get-relative-timestamp.ts

@@ -0,0 +1,33 @@
+export const getRelativeTimestamp = (date: Date): string => {
+    const now = new Date();
+    const seconds = Math.floor((now.getTime() - date.getTime()) / 1000);
+  
+    let interval = Math.floor(seconds / 31536000);
+    if (interval > 1) {
+        return `${interval}y`;
+    }
+  
+    interval = Math.floor(seconds / 2592000);
+    if (interval > 1) {
+        return `${interval}m`;
+    }
+  
+    interval = Math.floor(seconds / 86400);
+    if (interval >= 1) {
+        return `${interval}d`;
+    }
+  
+    interval = Math.floor(seconds / 3600);
+    if (interval > 1) {
+        return `${interval}h`;
+    }
+  
+    interval = Math.floor(seconds / 60);
+    if (interval > 1) {
+        return `${interval}m`;
+    }
+  
+    return `${seconds} seconds`;
+};
+
+export default getRelativeTimestamp;