feat: Support custom .parcelrc config

[mathieudutour]

Details

This PR introduces support for a custom .parcelrc at the root of the project. It will warn the user if the config doesn't extend Plasmo's one.

This serves as an escape hatch for things like https://github.com/PlasmoHQ/plasmo/issues/521 or https://github.com/PlasmoHQ/plasmo/issues/367.

Code of Conduct

• [x] I agree to follow this project's Code of Conduct
• [x] I agree to license this contribution under the MIT LICENSE
• [x] I checked the current PR for duplication.

Contacts

• Discord ID: 380325824286687233