AgentHost as a container + sample

[kostapetan]

Adds the distributed runtime as a container, to be used from samples and SDKs.
Adds a minimal hello sample using the runtime as container.

Why are these changes needed?

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• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.