Run GitHub publishing steps during unofficial pipelines

[lbussell]

This is a follow-up to https://github.com/dotnet/dotnet-docker-internal/issues/8105.

With the introduction of official/unofficial pipelines split, we'd like to exercise publish steps that reach out to GitHub during unofficial builds, if possible.

This includes:

• Publishing image info:

  docker-tools/eng/common/templates/jobs/publish.yml

  Lines 242 to 255 in 7841dec

  	- script: >
  	$(runImageBuilderCmd) publishImageInfo
  	'$(imageInfoContainerDir)/full-image-info-new.json'
  	'$(gitHubVersionsRepoInfo.userName)'
  	'$(gitHubVersionsRepoInfo.email)'
  	$(gitHubVersionsRepoInfo.authArgs)
  	--git-owner '$(gitHubVersionsRepoInfo.org)'
  	--git-repo '$(gitHubVersionsRepoInfo.repo)'
  	--git-branch '$(gitHubVersionsRepoInfo.branch)'
  	--git-path '$(gitHubImageInfoVersionsPath)'
  	$(dryRunArg)
  	$(imageBuilder.commonCmdArgs)
  	condition: and(succeeded(), eq(variables['publishImageInfo'], 'true'))
  	displayName: Publish Image Info

• Build notifications:

  docker-tools/eng/common/templates/jobs/publish.yml

  Lines 257 to 292 in 7841dec

  	# Task displayNames names are hardcoded to reference the task prefix used by 1ES official
  	# pipelines in eng/common/templates/1es-official.yml.
  	#
  	# These will fail if they are dependend on by an unofficial pipeline since they use a unique task
  	# prefix compared to official pipelines (see eng/common/templates/1es-unofficial.yml). This is
  	# acceptable because unofficial pipelines should not publish images.
  	#
  	# https://github.com/dotnet/docker-tools/issues/1698 tracks making this command no longer depend
  	# on individual step displayNames.
  	- script: >
  	$(runImageBuilderCmd) postPublishNotification
  	'$(publishNotificationRepoName)'
  	'$(branchName)'
  	'$(imageInfoContainerDir)/image-info.json'
  	$(Build.BuildId)
  	'$(System.AccessToken)'
  	'$(azdoOrgName)'
  	'$(System.TeamProject)'
  	$(gitHubNotificationsRepoInfo.authArgs)
  	'$(gitHubNotificationsRepoInfo.org)'
  	'$(gitHubNotificationsRepoInfo.repo)'
  	--repo-prefix '${{ parameters.publishConfig.publishAcr.repoPrefix }}'
  	--task "🟪 Copy Images"
  	--task "🟪 Publish Manifest"
  	--task "🟪 Wait for Image Ingestion"
  	--task "🟪 Publish Readmes"
  	--task "🟪 Wait for MCR Doc Ingestion"
  	--task "🟪 Publish Image Info"
  	--task "🟪 Ingest Kusto Image Info"
  	--task "🟪 Generate EOL Annotation Data"
  	--task "🟪 Annotate EOL Images"
  	--task "🟪 Wait for Annotation Ingestion"
  	$(dryRunArg)
  	$(imageBuilder.commonCmdArgs)
  	displayName: Post Publish Notification
  	condition: and(always(), eq(variables['publishNotificationsEnabled'], 'true'))

If possible, we should have a separate GitHub identity/App which has access to an internal/non-public repo that we can push these changes to.