HybridGateway - finalizers are added on not owned `HTTPRoute`s

[mlavacca]

Current Behavior

If an HTTPRoute points to a Gateway that does not exist or does not belong to KO, the HybridGateway controllers take ownership of that, regardless, by adding a finalizer.

Expected Behavior

If an HTTPRoute does not reference a Gateway managed by KO, KO's controllers should leave it untouched.