feat: enable WindowsProfile in defaults enforcement code flow

[jackfrancis]

Reason for Change:

Adds WindowsProfile into the standard defaults enforcement code flow. We retain the existing ARM parameters defaults to ensure back-compat defaults enforcement for pre-existing clusters.

This PR delivers the following opinionated defaults, which are subject to review:

// DefaultWindowsPublisher sets the default WindowsPublisher value in WindowsProfile
DefaultWindowsPublisher = "MicrosoftWindowsServer"
// DefaultWindowsOffer sets the default WindowsOffer value in WindowsProfile
DefaultWindowsOffer = "WindowsServerSemiAnnual"
// DefaultWindowsSku sets the default WindowsSku value in WindowsProfile
DefaultWindowsSku = "Datacenter-Core-1809-with-Containers-smalldisk"
// DefaultImageVersion sets the default ImageVersion value in WindowsProfile
DefaultImageVersion = "1809.0.20190314"

Previous defaults were:

WindowsPublisher = "MicrosoftWindowsServer" (unchanged in this PR)
WindowsOffer = "WindowsServerSemiAnnual" (unchanged in this PR)
WindowsSku = "Datacenter-Core-1809-with-Containers-smalldisk" (unchanged in this PR)
WindowsVersion = "latest" (this PR changes this value to an opinonated, dated version)

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jackfrancis]

We will not apply any defaults enforcement for pre-existing clusters.

[xizha162]

/LGTM

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[APPROVALNOTIFIER] This PR is APPROVED

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[codecov]

Codecov Report

Merging #1103 into master will increase coverage by 0.04%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master    #1103      +/-   ##
==========================================
+ Coverage   74.35%   74.39%   +0.04%     
==========================================
  Files         131      131              
  Lines       18274    18287      +13     
==========================================
+ Hits        13588    13605      +17     
+ Misses       3905     3903       -2     
+ Partials      781      779       -2

[mboersma]

lgtm pending Windows E2E tests

[jackfrancis]

@PatrickLang and @craiglpeters should sign off on this change, as it includes a change to the default Windows image version string we use to build Windows node vms.

[jackfrancis]

Welp. So much for this improving Windows 1.14 IIS flakiness.

@PatrickLang is this the image we expect from the 1809.0.20190314 reference?:

• Windows Server Datacenter 10.0.17763.379