Geo: Refactor Admin controllers to use Geo specific namespace

What does this MR do?

This fix a technical debt from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6452 (tracked here: https://gitlab.com/gitlab-org/gitlab-ee/issues/7126)

By moving Geo specific Controllers to its own namespace we are improving the code organization in our codebase.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/7126

Does this MR meet the acceptance criteria?

• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• EE specific content should be in the top level /ee folder