Merge branch 'docs-update-group-template-pricing-tier' into 'master'

Docs: Add premium & silver badge to group project templates docs

Closes gitlab-ee#11587

See merge request gitlab-org/gitlab-ce!28304

doc/user/group/custom_project_templates.md

-# Custom group-level project templates **[PREMIUM ONLY]**
+# Custom group-level project templates **[PREMIUM]**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/6861) in [GitLab Premium](https://about.gitlab.com/pricing) 11.6.