Image Block - add an accessibility label input to the link settings

[malalacharm]

Describe the bug
The Image/Image Box block fails accessibility audits when a link is applied to the block.

Image Box block: Has an aria-label, but it is incorrectly placed on the outer <div>
Image block: The linked <a> has no aria-label at all

To Reproduce
Steps to reproduce the behavior:

1. Add an Image Block
2. Add a Link to the block
3. Check on frontend
4. See error in Lighthouse ""Links must have discernible text"

Expected behavior
When a value is provided, the accessibility label should be applied directly to the generated <a> element, ensuring that the link has a discernible and accessible name.

For the Image Box block, the label should no longer be applied only to the outer <div> container. For the Image block, the label should be added to the linked <a> element.