MM-61947 Run DND expiry job more often and round expiry time to match interval (#29938)

* MM-61947 Run DND expiry job more often and round expiry time to match interval

* Move comment to make it godoc-compatible

* Change truncateDNDEndTime to work with seconds

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Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/platform/types/src/users.ts

@@ -100,6 +100,11 @@ export type UserStatus = {
     manual?: boolean;
     last_activity_at?: number;
     active_channel?: string;
+
+    /**
+     * The time when a user's timed DND status will expire. Unlike other timestamps in the app, this is in seconds
+     * instead of milliseconds.
+     */
     dnd_end_time?: number;
 };