chore: make the pipeline scripts in workshop locally executable

[ChunyiLyu]

Context

This is split out from #128.

In our workshop set up, learners cannot run the pipeline script locally and they can only test the pipeline script with a complicated docker build/run combo.This is adding unnecessary complication and friction to the workshop.

We should make the pipeline scripts locally executable: instead of docker build + docker run, we can just rewrite the scripts so they can be executed locally. To test, you just need to run the script (we can provide the input/output/metadata dir as env vars or arguments or assume test if /kratix does not exist).

A bit more context on this can be found in #128 (comment)

[ChunyiLyu]

cc @catmo-syntasso