Update Heartbeat check overview page (#1265)

* feat: update Heartbeat check overview page

* feat: test and update Heartbeat check ping examples

* feat: add Heartbeat check result info to Check results page

* feat: add link to check results to Heartbeat overview next steps

* feat: add back the tab titles

* feat: add Vercel cron job example

* feat: move ping examples to its own page

* feat: minor wording tweaks and move Vercel cron jobs section next to Node.js

* feat: remove video and move intro image further down the page

Author: guolau