Overhaul aggregated errors sent to Sentry

[unknwon]

Current dashboard looks like a messy and impossible (for me) to extract any useful/actionable information.

Work doc

[github-actions]

Heads up @tsenart - the "team/cloud" label was applied to this issue.

[unknwon]

I want to do some other smaller items first to wrap up from holiday, so hold on this until next week. New errors are being sent to Sentry for ~3 weeks now, we should have enough signals on how to improve further.

[unknwon]

Close in favor of https://github.com/orgs/sourcegraph/projects/139