Prevent downloading images by right-click

### Description

To avoid contents abuse, many media services prevent downloading images by right-click on their sites. For non-AMP pages, publishers use background_image CSS property to protect it and prevent right click download. However, for AMP pages, they need to implement the property for each image, and their CSS volume is growing up. Any plans to support the feature in the amp-image component?

### Alternatives Considered

Using background_image CSS property

### Additional Context

_No response_

Start by reviewing the amp-image component and the issue's proposed background_image alternative. Define the intended behavior for AMP images, including how right-click downloading should be handled, then identify the relevant tests and acceptance criteria before implementation.

Written by the indexing model from the issue text.