Generated image info file for internal builds contain incorrect information

[mthalman]

Builds that target internal builds of .NET now generate image info files to enable image caching. But the information in the file is technically incorrect because it's formatted to reference public builds. Examples:

• Digest value contains mcr.microsoft.com registry but the published image doesn't exist there.
• Commit URL references https://github.com/dotnet/dotnet-docker but the Dockerfile doesn't exist there