ARM Builder: Windows builds default to SSH communicator type when communicator is unset

[JenGoldstrich]

Similar to #415

Whenever the communicator field is unset Windows will try to connect via SSH instead of WinRM, this fails because SSH on Windows is not configured to work by default.

This happens because of this logic in the packer-plugin-sdk https://github.com/hashicorp/packer-plugin-sdk/blob/9c1d2437dcbde2571b2a8f5d8ce280dce76a377b/communicator/config.go#L461-L463

To solve this either force users to specify a communicator, or forcibly override the default to WinRM for Windows builds, this would need to be done before this Prepare call

packer-plugin-azure/builder/azure/arm/config.go

Lines 874 to 875 in 738e7ae

	var errs *packersdk.MultiError
	errs = packersdk.MultiErrorAppend(errs, c.Comm.Prepare(&c.ctx)...)