Add instructions to find the usage ping payload

What does this MR do?

This page: https://docs.gitlab.com/ee/user/admin_area/settings/usage_statistics.html says that the usage ping payload can be viewed in the Administration panel. But it takes quite a bit of searching to find the actual payload.

This MR is to add detailed directions to the actual payload in the Admin area.

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
• Link to e2e tests MR added if this MR has ~"Requires e2 tests" label. See the Test Planning Process.