fix(upgrades): set correct cluster_template_id

[mnaser]

It seems that fundamentally, we've relied historically on the code of Magnum
doing some form of 'inheritence' of the labels across clusters, however, the
reality is that it just copies everything over everywhere.

In order to make sure follow it, we stop checking parents (aka, check node
group if not found check cluster if not found check cluster template) and
instead rely on the label value directly configured. If the user used
merge labels then their values will be copied in, if they haven't, it will
copy their values in directly.

This fixes upgrades as well by making sure we set the correct cluster
template ID and copy all the labels, the main reason we had this issue
was because Magnum relied on the driver to copy the labels which we did
but we did not update the cluster template. So, cleaned that up and
added unit tests for coverage too.

Closes #317
Closes #325
Closes: #339

• fix: use labels from cluster directly
• fix: use labels from node group directly
• fix(upgrades): update cluster_template_id correctly