Add an end-to-end script runner example

[elliotgunton]

The script runner doesn't have a reproducible end-to-end example that includes at a minimum a Dockerfile, requirements.txt and the Python code in one folder. It would be good to help users get started with an example that can run on a local docker-desktop installation of Argo workflows (to simplify image repository needs).

e.g. minimal Dockerfile:

FROM python:3.12-slim

WORKDIR /app

COPY . .

RUN pip install --upgrade pip \
  && pip install hera

Issue motivated by slack conversation.