New badges (GitLab.com plans)

For #1906 (closed), follows #1902 (closed)

• Adds badges for GitLab.com plans (Free, Bronze, Silver, Gold)
• Available for release posts, features.yml, and comparison pages

New badges taken from https://gitlab.com/gitlab-org/gitlab-ce/issues/40350#note_51746460, designed by our UX team :)