Revert PowerShell modules to alpha (#4823)

## Change
We want to be able to publish both prerelease and release version of the
PowerShell modules. For ease of use, we will consistently have the
modules marked as prerelease here and only mark them as release as
needed in our official builds.

src/PowerShell/Microsoft.WinGet.Client/ModuleFiles/Microsoft.WinGet.Client.psd1

@@ -160,7 +160,7 @@ PrivateData = @{
         # ReleaseNotes = ''
 
         # Prerelease string of this module
-        # Prerelease = 'alpha'
+        Prerelease = 'alpha'
 
         # Flag to indicate whether the module requires explicit user acceptance for install/update/save
         # RequireLicenseAcceptance = $false

src/PowerShell/Microsoft.WinGet.Configuration/ModuleFiles/Microsoft.WinGet.Configuration.psd1

@@ -33,6 +33,7 @@
             )
             ProjectUri = 'https://github.com/microsoft/winget-cli'
             IconUri = 'https://aka.ms/winget-icon'
+            Prerelease = 'alpha'
         }
     }
 }

src/PowerShell/Microsoft.WinGet.DSC/Microsoft.WinGet.DSC.psd1

@@ -118,7 +118,7 @@
             # ReleaseNotes = ''
 
             # Prerelease string of this module
-            # Prerelease = 'alpha'
+            Prerelease = 'alpha'
 
             # Flag to indicate whether the module requires explicit user acceptance for install/update/save
             # RequireLicenseAcceptance = $false