✨ Feature: Allow Challenge Hosts to Purge Submissions Queue from Manage Tab

**Description:**
Currently, challenge hosts do not have the ability to purge the submissions queue from the **Manage** tab in EvalAI. This feature would allow hosts to clear out pending/running submissions for their challenge when necessary (e.g., stuck jobs, debugging, challenge resets).

**Proposed Solution:**

* Add a **“Purge Queue”** button to the Manage tab UI for challenge hosts.
* Clicking this button should:

* Prompt for confirmation (with clear warning: “This action will delete all pending submissions in the queue. This cannot be undone.”).
* On confirmation, call a backend API endpoint that purges the submissions queue for that challenge.
* Backend:

* Implement a new endpoint (accessible only by challenge hosts/admins) that clears all pending/running submissions for the given challenge.
* Ensure proper authorization checks to prevent misuse.

* UI/UX:

* Place the button in the Submissions/Queue management section.
* Provide success/error messages after action.
* * Shows the current number of submissions in the queue

**Benefits:**

* Helps challenge hosts quickly resolve issues like stuck queues.
* Reduces dependency on super-admins for manual purges.
* Improves host autonomy in managing their challenges.