Setup local docker-based development environment

Dockerfile

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+FROM ruby:3.0.0 as jekyll
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential \
+    git \
+    && rm -rf /var/lib/apt/lists/*
+
+# used in the jekyll-server image, which is FROM this image
+COPY docker-entrypoint.sh /usr/local/bin/
+
+RUN gem update --system && gem install jekyll && gem cleanup
+
+EXPOSE 4000
+
+WORKDIR /site
+
+ENTRYPOINT [ "jekyll" ]
+
+CMD [ "--help" ]
+
+# build from the image we just built with different metadata
+FROM jekyll as jekyll-serve
+
+COPY --from=jekyll /usr/local/bin/docker-entrypoint.sh /usr/local/bin/
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+# on every container start, check if Gemfile exists and warn if it's missing
+ENTRYPOINT [ "docker-entrypoint.sh" ]
+
+CMD [ "bundle", "exec", "jekyll", "serve", "--force_polling", "-H", "0.0.0.0", "-P", "4000" ]