Add an option to activate source only if a configuration is found in the project

[ndavd]

Issues

• [X] I have checked existing issues and there are no existing ones with the same request.

Feature description

My current use case would be the prettier linter. I am using eslint in a project and prettier is overriding it. So I tried doing only_local, but prettier is actually being installed in node_modules by a dependency of my project. As a workaround I tried adding a condition:

    condition = function(utils)
      return utils.root_has_file({
        '.prettierrc',
        '.prettierrc.json',
        '.prettierrc.yml',
        '.prettierrc.yaml',
        '.prettierrc.json5',
        '.prettierrc.js',
        '.prettierrc.cjs',
        '.prettierrc.toml',
        'prettier.config.js',
        'prettier.config.cjs',
      })
    end,

And this works 99% of the cases. Thing is that prettier also recognizes an entry inside package.json... So I feel like this would be a common thing to happen, maybe there should be an option to let the source decide whether it finds a configuration and activate it accordingly. Perhaps that's not possible, if that's the case then it would be nice to have a condition that allows me to check inside package.json for prettier (some util that let's us check inside files perhaps)