Allow to install this extension easily to Docker Lambda

[tmokmss]

In README, there is only instructions for zip Lambda. It would be great if we could install this extension to Docker Lambda easily.

IMO Lambda Web Adapter has great usability on Docker Lambda. Their usage is like the following:

# Dockerfile for Lambda function
FROM public.ecr.aws/docker/library/node:20-slim
# Just add this line to install the extension
COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.3 /lambda-adapter /opt/extensions/lambda-adapter
ENV PORT=7000
WORKDIR "/var/task"
ADD src/package.json /var/task/package.json
ADD src/package-lock.json /var/task/package-lock.json
RUN npm install --omit=dev
ADD src/ /var/task
CMD ["node", "index.js"]

The existing extension also requires some work to use it in Docker Lambda, so this can be a differentiator.

[simonmarty]

Captured in #17