The usage of the trusted-ip config resulted in a security incident that
allowed access to any oauth2-proxy protected endpoint without requiring
authentication.

Thankfully all significant endpoints had been protected by additional
measures such as network restrictions and are therefore not affected.
Only the prometheus and alertmanager endpoints have been exposed to the
public internet, but are not exposing sensitive data beyond metrics.

A check of the relevant logs didn't provide any indication of
compromise.

This patch replaces the third-party integration with the GitLab Native
integration for alertmanager alerts using webhooks.

This should play nicer with Alertmanager and GitLab and also resolve
issues, when the alert is marked as resolved or silenced.

References:
https://docs.gitlab.com/ee/operations/incident_management/integrations.html#add-integration-credentials-to-prometheus-alertmanager

It seems upstream has some problems with RWX volumes in longhorn 1.5.3
where share-mananger status isn't properly assessed and as a result not
restarted when single share-managers go down. The fix for now is to
manually patch the share-manager objects with an error state, which
triggers longhorn to repair itself.

In order to notice that, this alert triggers and allows to manually fix
the problem until a new upstream release is ready, that fixes the
problem.

References:
https://github.com/longhorn/longhorn/issues/7183#issuecomment-1823715359
https://github.com/longhorn/longhorn/wiki/Release-Known-Issues