fix(api): support repeating groups in bulk submission updates

[emaia]

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📣 Summary

The PATCH /api/v2/assets/{asset_uuid}/data/bulk/ endpoint was returning 500 error when the payload contained repeating group fields (arrays). Modified edit_submission_xml() to handle list values by replacing existing repeat elements with new ones from the payload. Fix #6638

📖 Description

Modified edit_submission_xml() to handle list values by replacing existing repeat elements with new ones from the payload. Added helper functions _edit_repeat_group() and _extract_relative_path() to process nested repeat group structures recursively.

💭 Notes

• Fix 500 error when bulk updating submissions with repeating group fields
• Add support for array values in the bulk update payload to update repeat groups
• Maintain backwards compatibility with existing simple field updates