Derive GitLab Employee badge from gitlab-com group

Summary

Currently, we determine if a user is a GitLab employee by checking the domain of the user's primary email.

This approach has a couple of problems, viz:

• Not all GitLab employees use GitLab email as their primary email
• There has been incidents in the past wherein non-GitLab employee were able to set their email with a gitlab.com domain
• There is no easy way to query

Proposal

One way to circumvent this problem, is to check if the user belongs to the gitlab-com group.

A more scalable option will be introduce concept of Employee-Organization model.

Refer to !28837 (comment 328910484) for detailed discussion.