Support for headless service

[andrew-demb]

Describe the feature

We created a headless service for our application and created a Canary resource to enable Flagger.

However, after creating Canary resources we found, that service resources created by Flagger are not headless services.

After a short investigation, we found this code: https://github.com/fluxcd/flagger/blob/9b39cf16f120cb4e2796bafca19d568ae2fdfaf3/pkg/canary/service_controller.go#L134

Which looks like a reset field to avoid errors on resource creation, but not for forbidding using headless services.

So the question is: is it intended not to preserve the headless service type?

Proposed solution

Check for the ClusterIP: None value to decide on the reset field ClusterIP value.

Any alternatives you've considered?

N/A