Update fetcher and make endpoint for fetching project versions

Please note --- this is for the 8.x-4.x branch

After the move to Gitlab, we needed to switch how we loaded project data. You can see this in 7.x-1.x here:

https://git.drupalcode.org/project/simplytest/blob/7.x-1.x/modules/simpl...

and

https://git.drupalcode.org/project/simplytest/blob/7.x-1.x/modules/simpl...

8.x-4.x has a new content entity for Projects: https://git.drupalcode.org/project/simplytest/blob/8.x-4.x/modules/simpl...

Most notably, this has a "versions" field. This should contain both the heads and tags from the resultant `git ls-remote` to the associating drupal.org project.

8.x-4.x also has a project fetcher to populate the version. This fetcher is using the old method and needs updated to use the `git ls-remote` logic. The old logic needs replaced with the new logic.

Once that is complete, there needs to be a new endpoint/controller that passes a version and can return the project's associated version. This will be consumed by the react application and should return JSON.

Ideally, the project versions can be cached for a given time interval (let's say 4 hours). After four hours, any request to the project fetcher for a specific project would reload it's version metadata.