update SDK build-push script to dynamically determine the example image path list

[KeranYang]

Summary

Currently, the paths to the example images are hardcoded in the build-push workflow and passed to the script. This means when adding a new or updating an existing example, a developer needs to make changes at two places, the example folder and the workflow YAML file. We can't guarantee that we always remember to update both, e.g. https://github.com/numaproj/numaflow-python/pull/186

If we can update the script to dynamically construct the list, it will solve the problem. The script can search the example folder looking for Dockerfiles to determine the image path list. This can be done for Go, Python, and Rust. Java is a bit different but we can also investigate.

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