Use library to provide deployment key for GitHub (#497)

* Use library to provide deployment key for GitHub

.azure/scripts/publish-performance-results.ps1

@@ -15,6 +15,9 @@ Copy-Item -Path $ResultsPath -Destination $GitPath -Recurse -Force
 git config user.email "quicdev@microsoft.com"
 git config user.name "QUIC Dev Bot"
 
+git config --global credential.helper store
+Add-Content "$env:USERPROFILE\.git-credentials" "https://$($env:MAPPED_DEPLOYMENT_KEY):x-oauth-basic@github.com`n"
+
 git add .
 git status
 

.azure/templates/publish-performance.yml

@@ -10,9 +10,9 @@ jobs:
   variables:
   - name: runCodesignValidationInjection
     value: false
+  - group: DeploymentKeys
   steps:
   - checkout: self
-    persistCredentials: true
 
   - task: DownloadBuildArtifacts@0
     displayName: Download Build Artifacts
@@ -31,3 +31,5 @@ jobs:
     inputs:
       pwsh: true
       filePath: .azure/scripts/publish-performance-results.ps1
+    env:
+      MAPPED_DEPLOYMENT_KEY: $(GitHubDeploymentKey)