Preview image with element polygon

Refs https://gitlab.com/arkindex/requests/-/issues/596

A fancy feature to quickly view an element (say text line) into its overall context (image, not element). This should be posisble without any backend dev as we do not need to find the best parent element (which would need some crazy heuristics on the backend side and will never be generic).

Here the feature would be trigerred on a single-click when:

• browsing elements (corpus level or children)
• in selection list

The button would open a modal or large popup that displays:

• the full image of the element in small resolution (400px width max for example)
• a bounding box (not the polygon) around the selected element