Support defining policies

Summary of the new feature / enhancement

Looking at existing Azure policies defined in https://github.com/Azure/azure-policy/blob/master/samples/GuestConfiguration/package-samples/configurations/AzureWindowsBaseline/AzureWindowsBaseline.mof, it seems that it may be useful to have a common Policy resource that can leverage use another resource for the actual get and set, but has a way within the config to have a custom test:

Here's an example policy in mof:

instance of ASM_Registry as $ASM_Registry26ref
{
	RuleId = "{a002b800-92a4-45cb-bbee-76c91739ddff}";
	AzId = "AZ-WIN-00175";
	BaselineId = "{982a79a8-1c46-4fdf-8cfd-60afedf7ad96}";
	OriginalBaselineId = "{9c2bc3d1-8668-48e5-ac5f-281718d52174}";
	Name = "Disable SMB v1 server";
	Severity = "Critical";
	Hive = "HKEY_LOCAL_MACHINE";
	Path = "SYSTEM\\CurrentControlSet\\Services\\LanmanServer\\Parameters";
	Value = "SMB1";
	Type = "REG_DWORD";
	ExpectedValue = "0";
	RemediateValue = "0";
	Remediate = true;
	AnalyzeOperation = "EQUALSORNOTEXISTS";
	ServerTypeFilter = "ServerType = [Domain Controller, Domain Member, Workgroup Member]";
	OSFilter = "OSVersion = [WS2008, WS2008R2, WS2012, WS2012R2, WS2016]";
	Enabled = true;
	ResourceID = "Disable SMB v1 server";
	ModuleName = "AzureOSBaseline";
	ModuleVersion = "1.0";
	ConfigurationName = "AzureOSBaseline";
};

Here's what it could look like in DSCv3:

name: Disable SMB v1 server
type: Microsoft.DSC/Policy
properties:
  audit:
    resource:
      type: Microsoft.Windows/Registry
      properties:
        keyPath: HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters
        valueName: SMB1
    expected:
      valueData:
          DWord: 0
    analyzeOperation: EqualsOrNotExist
  remediation:
    apply:
      _exist: false

In this example if the SMB1 property exists or doesn't equal 0, then the remediation is to delete it.

Proposed technical implementation details (optional)

No response

Start by reviewing the linked Azure policy example at samples/GuestConfiguration/package-samples/configurations/AzureWindowsBaseline/AzureWindowsBaseline.mof and compare it with the proposed DSCv3 YAML shape. Done means DSCv3 supports a policy resource that delegates get and set behavior while defining custom audit and remediation logic.