chore: adding license field to package.json

[georgewrmarshall]

Description

This PR adds a dual-license (MIT OR Apache 2.0) to the eslint-plugin-design-tokens repository. The license setup aligns with MetaMask’s open-source standards and ensures that external users can legally fork and utilize the plugin without license conflicts. Following guidance from our legal team, both LICENSE.MIT and LICENSE.APACHE2 files are added, and the package.json file is updated with the new license terms.

Related Issues

Fixes: #27

Manual Testing Steps

1. Verify the inclusion of LICENSE-MIT and LICENSE-APACHE files.
2. Check that package.json includes "license": "(MIT OR Apache-2.0)".
3. Confirm that all licensing terms match MetaMask’s open-source compliance requirements.

Pre-merge Author Checklist

• I’ve reviewed MetaMask Coding Standards for licensing requirements.
• I’ve included relevant license files in the root directory.
• I’ve confirmed that the package.json license entry follows the specified format.

Pre-merge Reviewer Checklist

• I’ve reviewed the included license files to ensure compliance.
• I’ve checked that the package.json entry accurately reflects the new license terms.
• All legal and compliance criteria are met for MetaMask’s open-source projects.