Bundling config with `XcodeBuildToolPlugin`

When creating a BuildToolPlugin.prebuildCommand it's possible to access context.package.directory which could include configurations or resource required to process the build command.

However XcodeBuildToolPlugin seems agnostic of the package it's being included with.

We wish to bundle a 'default configuration' with our XcodeBuildToolPlugin package which can also be overridden using the context.xcodeProject.directory

Such an example is defining a SwiftLint default_rule.yml which we'd like to distribute to multiple teams.

Since the config would be in deriveddata, it would be impossible to define parent_config:

parent_config: ../../assets/default_rule.yml