Post Terms: Add border block support

[akasunil]

What?

Add border block support to the Post Terms block.

Part of #43247

Why?

Post Terms block is missing border support.

How?

Adds the border block support in block.json

Testing Instructions

• Go to Global Styles setting ( under appearance > editor > styles > edit styles > blocks )
• Make sure that Post Terms block's border is configurable via Global Styles
• Verify that Global Styles are applied correctly in the editor and frontend
• Edit template/page, Add Post Terms block and Apply the border styles
• Verify that block styles take precedence over global styles
• Verify that block borders display correctly in both the editor and frontend

Watch attached video for more information.

Screenshots or screencast

Blog-Home-.-Template-.-gutenberg-.-Editor-.-WordPress.webm

[github-actions]

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Co-authored-by: akasunil <sunil25393@git.wordpress.org>
Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

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[ramonjd]

LGTM

Tested global styles and block level styles. The latter overrides the former.

I also add some border styles to core/post-terms in theme.json to makes sure it's overridden by global/block.

👍🏻