Introduce InventoryTemplates and NestedClusters

[ibrokethecloud]

Problem:

Improve hardware utilisation by allowing nested harvester clusters to be provisioned by seeder by using VM's and kubevirt BMC to allow VM's to be managed as inventory

Solution:

The PR introduces two new types

• InventoryTemplates - Allow a user to create and register VM based inventory in an existing seeder cluster. This is achieved by creating VM's from an InventoryTemplate and subsequently registering the VM's via Inventory construct in seeder. The VM's leverage kubevirt bmc to allow redfish/ipmi based power operations. InventoryTemplates can exist on their own, in which case they can be used like normal inventory by manually creating clusters
• NestedClusters - Allow a user to create Harvester clusters running in VM on top of existing Harvester clusters. NestedClusters leverage InventoryTemplates which allow users to define VMs managed as Inventory, and the newly provisioned Inventory is added to a cluster with the same name as NestedCluster. The lifecycle of InventoryTemplates in this case is managed by the NestedCluster, and deletion of NestedCluster will trigger cleanup of associated Cluster, InventoryTemplates, Inventory and VM's.

Related Issue(s):

Test plan:

Additional documentation or context

[khushboo-rancher]

This looks great!

[innobead]

@starbops @Vicente-Cheng @ihcsim Let's make progress on this PR, since QA is waiting for it to start working on running tests on the nested Harvester.

@ibrokethecloud please fix the conflict first.

cc @harvester/qa