Alert on FinalizeInvoice errors

[easyCZ]

When BillingService.FinalizeInvoice errors, alert on it.

[easyCZ]

To do this, it's not enough to alert on the FinalizeInvoice RPC (on gRPC), we also need to alert on the incoming webhook endpoint - that is on public-api-server

To do that, we need to track metrics from baseserver - #13040

[easyCZ]

Currently blocked on fixes to observability release pipeline.

[easyCZ]

Alerts are configured here - #13109
Runbooks are still needed.

[easyCZ]

Alert on stripe webhook: #13119
Runbook for stripe webhook: https://github.com/gitpod-io/runbooks/pull/391

Once these land, we can close this issue.

[easyCZ]

Alerting rules failed silently during deployment - #13255 fixes that

[easyCZ]

Alerts have now propagated.

[easyCZ]

This is now complete.