Consider merging the dotnet/dotnet-docker-nightly GitHub repo into the dotnet/dotnet-docker GitHub repo

I have often thought the dotnet/dotnet-docker and dotnet/dotnet-docker-nightly GitHub repos should be combined. aspnet/aspnet-docker was designed this way with the nightly assets stored in a separate branch (dev). The primary benefit of doing this is for merging and the traceability of changes in nightly to official. Given there is no merge support between repos, changes have to be manually copied. As part of this, you loose the commit history. Being able to browse the history is important at it allows users to see the reasoning/conversations/etc on changes. Granted this history isn’t really lost as you can go to the nightly repo to view the history. A secondary benefit is general enhanced visibility. It is more likely that users will see and contribute to incoming issues and PRs from the activity happening in microsoft/dotnet-nightly if it was happening in the dotnet/dotnet-docker GitHub repo where there are more eyes watching.

Work breakdown:

[x] Create Nightly branch in dotnet-docker GH repo
[x] Enable CI on nightly branch
[x] Move code from dotnet-docker-nightly repo to nightly branch
[x] Update build pipeline
[ ] Update maestro subscription and build definition
[x] Move active issues from dotnet-docker-nightly to dotnet-docker
[ ] Move active PRs from dotnet-docker-nightly to dotnet-docker
[x] Disable CI on nightly repo
[ ] Add dotnet-docker-nightly readme to redirect to dotnet-docker and archive repo.
[ ] Update microsoft/dotnet-nightly DH repo to reference dotnet-docker GH repo

dotnet / dotnet-docker-nightly

Consider merging the dotnet/dotnet-docker-nightly GitHub repo into the dotnet/dotnet-docker GitHub repo #525