fix: install @wordpress/eslint-plugin in toolkit by default

[nicholasio]

Related Issue/RFC: #

Description of the Change

@wordpress/eslint-plugin is an optional peer dep at eslint-config however toolkit must install it since it's what we use by default.

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• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.
• I have added a changeset to my PR. See CONTRIBUTING document for instructions

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Latest commit: e7e1f2c

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