Integrate download metrics in the new download page

Originally created by @sajolida on #14922 (Redmine)

Feature Branch: web/14922-download-metrics

Attachments

• successful-is-working.png
• download-iso-is-not-working.png
• 0002-Ensure-that-failing-to-record-a-hit-does-not-cause-o.patch
• 0001-Ensure-that-we-call-our-hit-counter-before-following.patch
• NetworkError on download and no refresh after installing extension.webm
• 0002-Cachebust-hits-to-the-counter.-re.-14922.patch
• 0001-Add-a-dummy-counter-file-to-ensure-that-regular-oper.patch
• 0001-Use-relative-URI-for-download-counter.-re.-14922.patch
• NetworkError on download button.webm
• 0002-Avoid-a-traceback-if-mirror-dispatcher.js-is-not-ava.patch
• 0001-Use-window.open-over-setting-window.location-to-avoi.patch

Related issues

• Related to #12127 (closed)
• Related to #15312 (closed)
• Blocks #16080 (closed)
• Blocks sysadmin#16009 (closed)