Refactor group path suggestion to Vue

In #356934 (closed) we partially fixed an issue with group path suggestions. But part of the issue is that there are two files doing similar things and conflicting with each other. These two files are app/assets/javascripts/group.js and app/assets/javascripts/pages/groups/new/group_path_validator.js.

We should refactor these files and related HAML to Vue so we can consolidate the logic and remove some legacy HAML/jQuery.