[EE] Ask user explicitly about usage stats agreement

What does this MR do?

It checks if it's only single-user deployment and if so it asks user for explicit agreement for enabling usage ping and version check. The banner is not displayed in the first week of use to give user some time to create more users.

This is EE backport of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21423 which disables banner if license is used.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?