feat: this changes the priority of theme overrides

[andrey-canon]

Description:

This is the migration pr for #1 issue

How to test

1. Clone frontend-platform repo into the src/mfe folder (repo frontend-platform=open-release/redwood.nelp from nelc repo)
2. Go to the main folder a run npm install
3. Add the module.config.js file into the frontend-app-learning folder

module.exports = {
    localModules: [
        { moduleName: '@edx/frontend-platform', dir: '../frontend-platform', dist: 'src' },
    ],
};

4. Restart the learning mfe service, docker attach container and then ctrl+c
5. checkout this branch
6. Follow the instructions of the original PR

[johanseto]

Working as expected