Add image-info publish for Go Docker images

[dagood]

.NET Docker publishes image info in dotnet/versions:
https://github.com/dotnet/versions/blob/main/build-info/docker/image-info.dotnet-dotnet-docker-nightly.json

This serves multiple purposes:

• Keeps track of last built base image digest + Dockerfile commit hash. If neither has changed, the next rolling build can skip building that particular image.
• Will be a place to store info for new rebuild features like Detect package updates and rebuild images dotnet/dotnet-docker#1455.
• Provides a place to see when new builds are being published without deep access into the infra.

The odd thing is dotnet/versions being a dotnet repo. But we can put it in dotnet/versions to start with, and move it later.

[dagood]

Initial stab at this was dotnet/versions#782, but we should wait until dotnet/dotnet-docker#3088 gets merged and we can uptake it. It lets us specify the image info file paths more directly. (With our unusual microsoft/main/microsoft/nightly branch names rather than just main, the paths were awkward.)

[dagood]

Done:

• dotnet/versions@de8d401
• https://dev.azure.com/dnceng/internal/_build/results?buildId=2491391&view=results