GitHub Package Registry - Downloads Badge

:clipboard: **Description**
Download count badges for packages hosted on the GitHub Package Registry

- Which service is this badge for e.g: GitHub Package Registry
- What sort of information should this badge show? Download counts, in whichever intervals the GitHub API makes available


:link: **Data**

- Is there a public API? Yes
- Does the API requires an API key? Auth should be used like our other GH services, specifically leveraging our [BaseGraphQlService](https://github.com/badges/shields/blob/master/core/base-service/base-graphql.js). The [RegistryPackageStatistics](https://developer.github.com/v4/object/registrypackagestatistics/) will be of use
- Link to the API documentation. https://developer.github.com/v4/

:microphone: **Motivation**
Because people want them! 😄 The motivation/benefits for the download badges for the GH Package registry is the same as the other registries we support

Refs https://github.com/badges/shields/issues/3608