investigate azure virtual machine size gen2 support

[soer3n]

It seems that currently only first-generation VM sizes are supported, unless an imageReference is configured in the Azure provider specification. However, we should support both first and second generation VM sizes once a VM size is specified.

This could also affect operating system manager.

[csengerszabo]

/label sig/cluster-management
/label customer-request
Internal reference: 8374

[csengerszabo]

Related dashboard issue: kubermatic/dashboard#7605

[csengerszabo]

Resolution: having a logic for handling the imageReference (right now it’s part of the Machine Deployment specification), by mutating the machine deployment (defaulting for gen1/2) in machine-controller. In the UI, we also need to be able select the imageReference, and configure the Machine Deployment directly.