Comment Template: Add Border Block Support

[shail-mehta]

What?

Add border block support to the Comment Template block.

Part of #43247

Why?

Comment Template block is missing border support.

How?

Adds the border block support in block.json.

Testing Instructions

• Go to Global Styles Settings ( Under Appearance > Editor > Styles > Edit styles > Blocks ).
• Make sure that Comment Template block's border is Configurable via Global Styles.
• Edit Template/Page & Add Comment Template block and Apply the border Styles.
• Verify that Comment Template block styles take precedence over global Styles.
• Verify that Comment Template block borders display correctly in both the Editor and Frontend.

Screenshots or Screencast

add-border-support-in-comment-template.mp4

[github-actions]

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Co-authored-by: shail-mehta <shailu25@git.wordpress.org>
Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

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[ramonjd]

LGTM

Border styles are output by global styles :root :where(.wp-block-comment-template), and overridden by block-level inline CSS.