Update for KeyVault CODEOWNERS

[Adriano Arce (adarce)]

This adds the azure-sdk-write-keyvault team as code owners, removing lgonsoulin.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR updates the CODEOWNERS file to replace individual maintainer @lgonsoulin with the @Azure/azure-sdk-write-keyvault team across KeyVault SDK ownership entries, ensuring team-based ownership for better maintainability.

• Adds @Azure/azure-sdk-write-keyvault team to AzureSdkOwners, ServiceOwners, and PRLabel sections for KeyVault
• Removes individual maintainer @lgonsoulin from ServiceOwners
• Maintains existing owners while transitioning to team-based ownership model

[Laia Patiño (laiapat)]

LGTM