Update common Docker engineering infrastructure with latest

Author: dotnet-docker-bot

eng/common/templates/variables/docker-images.yml

@@ -1,5 +1,5 @@
 variables:
-  imageNames.imageBuilderName: mcr.microsoft.com/dotnet-buildtools/image-builder:2766581
+  imageNames.imageBuilderName: mcr.microsoft.com/dotnet-buildtools/image-builder:2776519
   imageNames.imageBuilder: $(imageNames.imageBuilderName)
   imageNames.imageBuilder.withrepo: imagebuilder-withrepo:$(Build.BuildId)-$(System.JobId)
   imageNames.testRunner: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux3.0-docker-testrunner

eng/common/templates/variables/dotnet/secrets-unofficial.yml

@@ -0,0 +1,5 @@
+variables:
+- group: DotNet-Docker-Secrets-Unofficial
+
+- name: dockerHubRegistryCreds
+  value: --registry-creds 'docker.io=$(dotnetDockerHubBot.userName);$(BotAccount-dotnet-dockerhub-bot-PAT)'