Support azd package for containerized apps that don't use docker build

[ellismg]

When using dotnet publish or ACR remote builds for a container based service, azd package doesn't end up producing an artifact that you could use later. Even in the case of docker build the package output is usually just the name of the tagged image, not something like the output of docker save or the like, so there's no first-class artifact to transfer to another machine.

We've discussed what we might do here a bit in #4573 (comment) when we were landing dotnet publish based build and pushing for containerized applications.

This only impacts the ability to use azd package to produce an artifact that you can deploy later. Both azd up and azd deploy are not broken due to the lack of first-class package artifact.