Expose metadata in readPackage hook

[DerYeger]

• I'd be willing to implement this feature (contributing guide)

Describe the user story

As a developer, I often want to implement hooks for my local packages only, but I often face the issue that I cannot resolve (or otherwise trivially identify) packages of my monorepo in the readPackage hook.

Describe the solution you'd like

Add more metadata to the context parameter of the readPackage hook, including a boolean field indicating that pkg is a local package of a monorepo (or the root).

Describe the drawbacks of your solution

I cannot identify any drawbacks.

Describe alternatives you've considered

Hardcoding an array of local packages.
It's obviously not possible to resolve the package.json of a package in the hook.