fix contour prom query for when service name is overwritten

[BrandonCate]

Problem:
When the Canary.Spec.Service.Name field is used to override default generated name the corresponding prom queries fail to return anything during the canary analysis phase due to an incorrect envoy_cluster_name

Fix:
The envoy_cluster_name is based off of the service name and so the service name is used instead of the target name (targetRef.Name)

Note:
Unsure if this is a similar problem for all envoy based controllers

[aryan9600]

Thanks for the PR 🙇
Just have one small nitpick.

[aryan9600]

I'd imagine this problem exists with all other providers that use Envoy, like Kuma, Gloo, etc. If you'd be willing to modify this PR to fix and test those as well, that'd be great 😄

[BrandonCate]

@aryan9600 updated with suggestions
And can we open up a separate issue for the other providers that use envoy and work it from there? I don't mind doing it when I have spare time, but it will take me a little longer just because I'm less familiar with the other providers

[aryan9600]

Could you please squash all three commits into one with the message fix contour prom query when service name is specified. Thanks!

[BrandonCate]

squashed