Include cluster name in all alerts

[ashokhein]

We have a single Slack channel to send all notifications from all environments. A few alert messages can't be identified from which environment.

x-service.namespace
Canary analysis completed successfully, promotion finished.

y-service.namespace
Canary analysis completed successfully, promotion finished.

z-service.namespace
Canary analysis completed successfully, promotion finished.

I want to include the cluster name in all alerts so the expected behaviour

x-service.namespace
Cluster
ClusterName
Canary analysis completed successfully, promotion finished.

y-service.namespace
Cluster
ClusterName
Canary analysis completed successfully, promotion finished.

z-service.namespace
Cluster
ClusterName
Canary analysis completed successfully, promotion finished.

Signed-off-by: ashokhein ashokhein@gmail.com

[stefanprodan]

LGTM

Thanks @ashokhein