Enhance Jetpack integration for comment meta sync

[obenland]

Fixes #1059.

Adds the required sync information to make like and repost notifications work for Jetpack and WoA sites.

Proposed changes:

• Adds filters to include ActivityPub comment meta keys and custom comment types in Jetpack sync.

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Can only be tested in conjunction with changes on WordPress.com.

Changelog entry

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Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

Updated sync allowlist to add support for Jetpack notifications of likes and reposts.

[Copilot]

Pull Request Overview

This PR enhances the Jetpack integration to enable ActivityPub comment synchronization for likes and repost notifications on Jetpack and WordPress.com sites.

• Adds comment meta synchronization filtering to include ActivityPub-specific metadata
• Implements comment type registration for proper sync handling during early WordPress hooks
• Extends existing sync functionality to cover comment-related data alongside post data

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[pfefferle]

No idea how to test, but I fully trust you in everything what you do! 🤜🤛