[Openstack] Make it possible to mix worker nodes flavors

[huxcrux]

What would you like to be added:
The possibility to mix flavors of worker nodes.

I think this could be defined as a object.

{
  flavor = "xxxxx"
  amount  = 3
  label = "gpu nodes"
},
{
  flavor = "xxxxx"
  amount  = 3
  label = "workers"
},
{
  flavor = "xxxxx"
  amount  = 3
  label = "cron nodes"
}

Preferably different groups of nodes would have their own server group (if created)

Why is this needed:
I can find multiple reasons for this, some examples below:

1. The possibility to add nodes with different capabilities, Example GPU nodes
2. Have smaller or larger nodes for cronjobs

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[huxcrux]

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