Support BaseContainerRepository as a prefix for ContainerRepository

[scrocquesel-ml150]

I would want to be able to publish multiple projects in a sln with just a single command.

dotnet publish -p:ContainerRegistry=xxx.azurecr.io -p:BaseContainerRepository=$(System.TeamProject)/$(Build.Repository.Name)

I know I can add some properties, but this use case seems to be a reasonable pattern for being supported out of the box from the command line only.

I think that if BaseContainerRepository is not empty it should be prefixed to ContainerRepository wether it is the default AssemblyName value or custom value.

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