Restructure Guardr to follow repo setup and install patterns like other existing distros

Problem/Motivation

The Guardr project is a distribution and profile combined. This was common practice with Drupal 7 distributions, however many notable Drupal 8 distributions break out the one-time install Drupal install from the install profile and other components such as config in Guardr Core.

The Guardr team would like to structure Guardr in a similar fashion to these other modern Drupal 8 distributions to fit two common use cases:

1. One time Drupal 8 install with Guardr dependencies and configuration. From there the site owner would manage Drupal updates per standard Drupal documentation.
2. Use Guardr as a dependency within existing or other new projects leveraging their own install profiles.

Distributions we referenced for ideas: Lightning Project, Drupal Commerce Project Base, and Thunder Project (All three of these projects also exist in Packagist)

Proposed resolution

1. Create new Guardr Project in Github that acts as a starter for the one-time Drupal 8 install of Guardr
2. Convert existing Guardr d.o project to contain just the install profile for Guardr and associated composer.json
3. Use existing Guardr Core d.o project as a module (current setup) and add composer.json
4. Publish Guardr Project on Packagist so composer create-project can be leveraged

Current plans are to make Guardr and Guardr Core on d.o direct dependencies of Guardr Project on Github.