The dynamic client returned for unit tests may not be smart enough to
automatically guess the APIVersion and Kind (which the real kube-apiserver can
handle automatically). To get over this, we can simply simply include these when
creating the objects.

… API types.

Clusters may not always have the v1 CRDs installed. This means gwctl will have
to use whatever version is available in the cluster. Hence, we will use API
Discovery to determine the "preferred" API version as per the kube-apiserver and
then use a dynamic client to fetch that specific versioned resource.

Once that specific versioned resource is fetched (e.g. v1beta1.Gateway), it will
be converted to a concrete type used within gwctl (eg. v1.Gateway), which will
usually be a more newer/stable version. For most cases, this conversion should
not result in any losses. If in the future, a need arises for such special
cases, we should be able to extend the approach by configuring some conversion
functions (eg. conversion function for v1beta1.Gateway -> v1.Gateway).

…Gateway API types.