feat: Add support for multipart message editing [WPB-22309]

[thisisamir98]

WPB-22309 [Web] Multipart message edit protocol update

Pull Request

Summary

• What did I change and why? Added support for building multipart edit message.
• Risks and how to roll out / roll back (e.g. feature flags): none.

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Security Checklist (required)

• [X] External inputs are validated & sanitized on client and/or server where applicable.
• [X] API responses are validated; unexpected shapes are handled safely (fallbacks or errors).
• [X] No unsafe HTML is rendered; if unavoidable, sanitization is applied and documented where it happens.
• [X] Injection risks (XSS/SQL/command) are prevented via safe APIs and/or escaping.

Accessibility (required)

• [X] I have read and this PR upholds our Accessibility Best Practices.

Standards Acknowledgement (required)

• [X] I have read and this PR upholds our Coding Standards and Tech Radar Choices.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud