Image block: Add border style support

[carolinan]

What?

In these two uses there is a suggestion to revisit the decision to exclude the border style option from the image block.

#47401
#43247

The decision to exclude the border style was made in 2021.
#31366 (comment)

This PR adds the border style to block.json of the image block.

Testing Instructions

Test the border style options with different image block settings and when the image block:

1. is a placeholder
2. is nested
3. is linked
4. has lightbox enabled
5. is aligned
6. has duotone
7. has the rounded block style applied

Style the block both from the Styles sidebar in the Site Editor and in the block editor.

Confirm that the border style is inline on the block.

[github-actions]

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Co-authored-by: carolinan <[email protected]>

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