Docker image is working on x64 host machines only

[alzimmermsft]

I built a local docker image following the README.
However, azmcp binary failed to start in the resulting container on my Mac M4 machine.
There are hard-coded target platforms in Dockerfile (example).
When I changed x64 to arm64, everything worked fine.

Ideally, docker image should be platform agnostic and compatible with different architectures.
Link: https://docs.docker.com/build/building/multi-platform/

[alzimmermsft]

Copied from Azure/azure-mcp#273