Migrate preview button in group templates

What does this MR do and why?

Migrate preview button in group templates

What does this MR not do?

Migrate the radio input label currently masquerading as a button

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Follow instructions in https://docs.gitlab.com/ee/user/group/custom_project_templates.html#set-up-group-level-project-templates
• Create a new project in group (create from template > go to Group tab, see Preview button

Links

• ✂️ UX Paper Cuts 16.9 → Pajamas Migrations (#430246 - closed)