Preserve existing store labels when updating attribute option via API

[mimou78]

Description (*)

This PR fixes an issue where updating a product attribute option via the API endpoint:

PUT /V1/products/attributes/byAttributeCode/options/byOptionId

would unintentionally erase store-specific labels that were not included in the payload.

Magento's current implementation of \Magento\Eav\Model\Entity\Attribute\OptionManagement::saveOption() overwrites all store_labels for an option when updating just one, instead of merging them. This fix introduces logic to preserve existing store labels and only update those explicitly provided.

Related Pull Requests

Fixed Issues (if relevant)

1. Fixes Attribute Option Label Gets Overwritten When Updating Store Labels #40093

Manual testing scenarios (*)

1. Create an attribute option with multiple store labels (e.g., for France and Germany).
2. Use the API to update only one store label:

 {
     "option_id": 1234,
     "store_labels": [
       {
         "store_id": 2,
         "label": "Bleu updated"
       }
     ]
   }

3. Use the API again to update another store label only:

{
  "option_id": 1234,
  "store_labels": [
    {
      "store_id": 3,
      "label": "Blau updated"
    }
  ]
}

4. Expected result: both store labels (store 2 and store 3) remain intact and updated accordingly.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[mimou78]

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[mimou78]

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[mimou78]

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[mimou78]

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[mimou78]

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[mimou78]

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[mimou78]

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[mimou78]

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