Add license package metadata

[wangedmund77-cmyk]

Summary

• adds missing npm support/discovery metadata for @inrupt/solid-client-errors
• updates only package.json

Metadata added

• license: MIT

Validation

• parsed package.json as JSON after the change
• confirmed the manifest still has name: @inrupt/solid-client-errors
• checked this is metadata-only: no runtime code, dependencies, exports, generated assets, or build behavior changed

This small metadata fix makes the published npm package expose the project support/discovery information once the package is next released.