feat: add flagger canary support

[daviddelucca]

Context

We are using Kubedog in our pipeline to watch rollouts and now we are moving to Flagger to have Canary Deployment but Kubedog doesn't support it.

Proposal

Since Flagger is a popular operator for Kubernetes, we would like to add support to Flagger Canary. The changes are isolated: we have created a new tracker specific for Canary so it won't impact in other resources.

My only concern is just about a custom specific configuration for Canary:

func setDefaultCanarySpecValues(spec *MultitrackSpec) {
	setDefaultSpecValues(spec)
	*spec.AllowFailuresCount = 0
}

In a Canary deployment, we don't want to "keep trying" a rollout: if it fails, it must stop. Also I don't think it's a good idea to let people pass AllowFailuresCount because could lead a mistakes like eternal loopings.

[fandujar]

Solves #173

[distorhead]

Hi! This looks like a very good starting point of supporting flagger Canary, because it is already useful to determine Canary readiness.

The next step could be adding detailed subtrackers for Deployments (and consequently Pods) that Canary creates during its operation, show logs of some pods etc.

Thanks! 👍

[distorhead]

What about AllowFailuresCount, I think it is ok to omit this param for Canary. Maybe we need to refactor (a little bit later) MultitrackSpec params and make a separate supported options structs for each resource kind.