Handle CNAME leafs corretly

[maksymvavilov]

What

When probing CNAMEs we return the first occurrence of a healthy IP response or the last of an unhealthy.

How

The logic here in question.
Decide if we want to change the way we deal with CNAMES. If yes, reimplement the logic in question.

[maksymvavilov]

While at it we could remove lastCheckedAt from the probe CRD and convert it to the local var. Or at least don't write unexisting field to the CR