Feature request for az vm repair: Optionally Specify OS of Rescue VM

### Extension name (the extension in question)
Repair

### Description of issue (in as much detail as possible)
I recently helped someone use az vm repair to help create a rescue vm for their source VM, an appliance running custom Linux. Since it was detected as a Linux VM, the repair VM was an Ubuntu box, which is specified per the documentation. However, the user needed the Rescue VM to be a Windows Server 2016+ with Hyper-V functionality in order to correct his particular issue, so we had to delete this rescue VM and manually create a WS2016 rescue VM. Thus, I propose an optional switch that gives the option for your Repair VM to be either Windows or Linux. By default it could be how it is currently (Windows Server repair VM for Windows source VMs, Ubuntu repair VMs for Linux source VMs), but if the switch is enabled, we can either

1. Specify if we want "Windows" or "Linux"
2. Maybe specify the exact Marketplace image we'd like our Rescue VM to be (I can imagine this being more of a headache to implement)

Thank you for your consideration!

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#### Document Details

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* ID: a0c5cd11-36e0-b233-4f0c-3d432a9925a1
* Version Independent ID: 99b6e064-4f75-9cce-b6e0-0ad1943552b9
* Content: [az vm repair](https://docs.microsoft.com/en-us/cli/azure/ext/vm-repair/vm/repair?view=azure-cli-latest#ext-vm-repair-az-vm-repair-create)
* Content Source: [latest/docs-ref-autogen/ext/vm-repair/vm/repair.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/master/latest/docs-ref-autogen/ext/vm-repair/vm/repair.yml)
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**