OpsGenie cross-team deduplication - alias prefix

OpsGenie has built in deduplication of alerts.
This is a problem for us because we have multiple teams using the same OpsGenie account (different teams).
Deduplication is based on the opsGenie alias field. This field is set to the alertmanager alert key.Hash.
This means that if two teams have the same alert key, they will be deduplicated even if they are different alerts.

As a result, we have alerts which are only sent to one team, but are deduplicated on another team. The same can happen for resolving alerts. If the alert is resolved in the team that did not receive the alert, it will not be resolved in the team that did receive the alert and stay open until it is resolved manually.

One workaround is to configure a prefix for the Promtheus Integration in OpsGenie. This will add the prefix to the alias field. This will prevent deduplication between teams.
Unfortunately, this does not support updating summary and description fields (config: update_alerts).

Another workaround is to change the "group by" rules in alertmanager and add another label, e.g. team. But this configuration is error prone.

Proposed solution:
Add a new field to the OpsGenie integration configuration in alertmanager. This field will be added to the alias field. This will allow us to configure a prefix for the alias field and prevent deduplication between teams.

It will also allow use cases where the alerts from different monitoring clusters should not be deduplicated. https://github.com/prometheus/alertmanager/issues/1598

Start by locating the OpsGenie integration configuration and the code that sets the alias from the alert key hash; review how the existing update_alerts option is handled. Add the requested configurable alias prefix and verify that alerts from different teams or clusters no longer deduplicate while update behavior remains supported.