Keep track of DRIs for frontend dependencies within GitLab

@leipert and I were discussing a way to resolve gitlab-org/frontend/rfcs#21 (closed) by migrating the remainder of our frontend dependencies into RenovateBot. Since maintaining a large config file within the renovate-gitlab-bot repository is going to become increasingly brittle, we are proposing the creation of a simplified configuration which can live within the GitLab repo itself.

The primary benefit of doing this would be to allow a linting tool to ensure parity with the dependencies listed in packages.json. We can also ensure that DRIs are designated for each dependency so that someone is responsible to keep things up-to-date. The addition of new dependencies will require further scrutiny as someone will be required to accept responsibility to maintain it going forward.

Here is an example config schema we could use (in yaml):

- group: 'Webpack related dependencies'
  description:
  dri:
    - '@mikegreiling'
    - '@leipert'
  packages:
    - copy-webpack-plugin
    - css-loader
  renovate:
    groupMajor: false
    enabled: false

- group: 'Not owned'
  packages:
    - all of them

We would like to create a POC for this in the following steps:

1. Create yml file encompassing all of the currently configured dependencies within renovate-gitlab-bot
2. Add a linting script to ensure all package.json entries have corresponding entries in this config file
3. Modify renovate-gitlab-bot to consumer this config file
4. Start configuring DRIs for all un-assigned dependencies