[Feature Request]: Document how xlang users should avoid a mismatch between expansion environment and runtime environment

### What would you like to happen?

Users who use custom containers + external transform will likely run into expansion environment+runtime environment mismatch issues, unless expansion happens in the same or compatible environment.

We should explain and/or make it simple how users can avoid this mismatch. For example, users could be running expansion server boot binary on in a container built from a custom image that has the same base image as sdk harness (runtime) image.

### Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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