Lets users to download usage data as json file
Implementation for proposal: gitlab-org/gitlab#346372 (comment 810062175)
Problem
We're creating a separate page so users will be able to review, redact and submit usage ping.
We want to let users to download usage data json file for manual submitting.
Result
Add a new button “Export Payload” as json. It will send GET /usage_data.json for data export. Send response as a file.