Story ads: move the ads badges to the bottom of the page

### Summary

This issue proposes to move the ad badge in story to the bottom of the page.

### Design Document

It's not a big change. See examples below:

After

Before

### Motivation

The top of the story page is unusually cluttered. The progress bar and the open source player's action buttons are placed on top. Currently, the ad badge overlaps with these buttons, making it very difficult to see. Therefore, we are rethinking holistically where the badge should be placed, and came up with this new design.

### Alternative Solutions

If we are not in favor, we may keep the existing design.

### Launch Tracker

_No response_

### Notifications

/cc @ampproject/wg-approvers @ampproject/wg-stories