Injector: Change order for generating service.istio.io/canonical-name

[SebastianJ91]

Wouldn't it be better to change the injection template to use app.kubernetes.io/instance with a higher priority than app.kubernetes.io/name. This would allow multiple instances of the same app to coexist in the same namespace, without mixing their metrics.

This was already discussed in #10724 but was finally done without app.kubernetes.io/instance in mind.

This could easily be changed in the template, but could lead to changes in existing environments :

istio/manifests/charts/istiod-remote/files/injection-template.yaml

Line 36 in ef08bf9

service.istio.io/canonical-name: {{ index .ObjectMeta.Labels `service.istio.io/canonical-name` | default (index .ObjectMeta.Labels `app.kubernetes.io/name`) | default (index .ObjectMeta.Labels `app`) | default .DeploymentMeta.Name | trunc 63 | trimSuffix "-" | quote }}

could be changed to

service.istio.io/canonical-name: {{ index .ObjectMeta.Labels `service.istio.io/canonical-name` | default (index .ObjectMeta.Labels `app.kubernetes.io/instance`) | default (index .ObjectMeta.Labels `app.kubernetes.io/name`) | default (index .ObjectMeta.Labels `app`) | default .DeploymentMeta.Name  | trunc 63 | trimSuffix "-" | quote }} 

Also documentation would need to be changed.

For now my workaround is to set service.istio.io/canonical-name manually, which has the highest priority.