Upgrade Sentry to Latest version (20.10.1) from 9.1

Sentry logs all the 500 errors for GitLab.com yet those errors are not being routed to the appropriate teams and parts of the application are failing. Engineering teams are finding out about these problems when customers or internal users complain, NOT by any notification.

The latest Sentry has significantly improved notification capabilities, that should help us route 500 errors to the proper engineering team, to reduce the number of 500 errors and broken functionality.

This issue is to upgrade Sentry to the latest version so we can decrease the time to resolve production bugs and errors.