Remove example PFX files from repo (#275)

This PR removes the example PFX files in the repo and makes them
available to CI/PR if necessary.

Closes #269 

###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/microsoft/react-native-xaml/pull/275)

.github/workflows/template-buildexample.yml

@@ -11,6 +11,10 @@ on:
         required: false
         default: 'example'
         type: string
+      useBuildCertificate:
+        required: false
+        default: false
+        type: boolean
 
 jobs:
   build-example:
@@ -25,8 +29,25 @@ jobs:
     - name: build TS
       run: yarn build
 
+    - name: Decode the pfx
+      if: ${{ inputs.useBuildCertificate }}
+      run: |
+        $PfxBytes = [System.Convert]::FromBase64String("${{ secrets.EXAMPES_BASE64_ENCODED_PFX }}")
+        $PfxPath = [System.IO.Path]::GetFullPath("${{github.workspace}}\GitHubActionsWorkflow.pfx")
+        Write-Host $PfxPath
+        [System.IO.File]::WriteAllBytes("$PfxPath", $PfxBytes)
+      working-directory: ${{ inputs.exampleName }}
+
     - name: yarn windows
-      run: yarn windows --no-launch --no-deploy --no-packager --logging
+      run: yarn windows --no-launch --no-deploy --no-packager --logging ${{ inputs.useBuildCertificate && '--msbuildprops PackageCertificateKeyFile=${{github.workspace}}\GitHubActionsWorkflow.pfx' || '' }}
+      working-directory: ${{ inputs.exampleName }}
+
+    - name: Remove the pfx
+      if: ${{ inputs.useBuildCertificate }}
+      run: |
+        $certificatePath = [System.IO.Path]::GetFullPath("${{github.workspace}}\GitHubActionsWorkflow.pfx")
+        Write-Host $certificatePath
+        Remove-Item -path $certificatePath
       working-directory: ${{ inputs.exampleName }}
 
     - name: test app

example/windows/example/example.vcxproj

@@ -14,8 +14,6 @@
     <AppContainerApplication>true</AppContainerApplication>
     <ApplicationType>Windows Store</ApplicationType>
     <ApplicationTypeRevision>10.0</ApplicationTypeRevision>
-    <PackageCertificateKeyFile>example_TemporaryKey.pfx</PackageCertificateKeyFile>
-    <PackageCertificateThumbprint>75F170D34994859553AF5C50C18A9AECDD312B27</PackageCertificateThumbprint>
   </PropertyGroup>
   <PropertyGroup Label="ReactNativeWindowsProps">
     <ReactNativeWindowsDir Condition="'$(ReactNativeWindowsDir)' == ''">$([MSBuild]::GetDirectoryNameOfFileAbove($(SolutionDir), 'node_modules\react-native-windows\package.json'))\node_modules\react-native-windows\</ReactNativeWindowsDir>
@@ -152,7 +150,6 @@
   <ItemGroup>
     <None Include="..\..\App.tsx" />
     <None Include="..\..\index.js" />
-    <None Include="example_TemporaryKey.pfx" />
     <None Include="packages.config" />
     <None Include="PropertySheet.props" />
     <Text Include="readme.txt">

examplenuget/windows/examplenuget/examplenuget.vcxproj

@@ -15,8 +15,6 @@
     <ApplicationType>Windows Store</ApplicationType>
     <ApplicationTypeRevision>10.0</ApplicationTypeRevision>
     <ReactNativeWindowsAllowNugetNpmMismatch>true</ReactNativeWindowsAllowNugetNpmMismatch>
-    <PackageCertificateKeyFile>examplenuget_TemporaryKey.pfx</PackageCertificateKeyFile>
-    <PackageCertificateThumbprint>CA08428B1920E77BE093E559694FE56031D6E5E9</PackageCertificateThumbprint>
   </PropertyGroup>
   <PropertyGroup Label="ReactNativeWindowsProps">
     <ReactNativeWindowsDir Condition="'$(ReactNativeWindowsDir)' == ''">$([MSBuild]::GetDirectoryNameOfFileAbove($(SolutionDir), 'node_modules\react-native-windows\package.json'))\node_modules\react-native-windows\</ReactNativeWindowsDir>
@@ -152,7 +150,6 @@
     </Midl>
   </ItemGroup>
   <ItemGroup>
-    <None Include="examplenuget_TemporaryKey.pfx" />
     <None Include="packages.config" />
     <None Include="PropertySheet.props" />
     <Text Include="readme.txt">